I'm commuting now on a rigid 29er with mid-drive. I'm finally wearing out the rear tire, and need to get a replacement, so I'm looking for recommendations.
Bike: Giant Toughroad w/ BBS02 conversion, rack and panniers (60lbs loaded)
Rider weight: 160 lbs
Riding conditions: Mixed road and path. No snow, minimal rain.
Size: 29x2.0-2.2 (would like to stay above 45mm).

Priorities (in order):
1) Traction and ride quality
2) Lower rolling resistance
3) Tubeless
4) Flat protection

My current tires are the stock Maxxis Silkworms, that are acceptable, but they're slow. A good gravel tire could work, but most of those seem to be about 35mm. I would prefer the larger tire just so it's easier for off-roading. Smooth tread is ok, but I think some mild tread may be beneficial for my riding.
I'm currently thinking something like a Continetal Race King or Schwalbe Thunder Burt, what else should I be looking for?

There's a treaded version of the Marathon, right? Which means there's also probably a Continental version to compete with it.

The Continental Speed Kings are a good option. They're low rolling resistance but may wear out quickly with your e-assist. I'm planning on getting some for my 29er (no motor) for city riding, set up tubeless.

Thanks, those look like a good option. Wear probably isn't a huge issue, I'm probably looking at about 2k mi/year.

It's not just the mileage but the power that the motor plus your legs put out: it can wear out tires more quickly. The BBHSD motor probably would be even more likely to shred rear tires quicker. If you need more tread, look at the Schwalbe racing ralph 29er tires. I'm using them on my full suspension Mtb and find them quite nice.

Teravail Ramparts. They come in "light and supple" and in "durable." And also in tan sidewall.

I know you would like to stay at a 45mm min, but Bontrager GR1 Team issue Gravel Tire in 40mm is a nice tire. Tubeless, rides on the road nicely, handles the paths well. Good all around tire.

1) Not sure what you mean by traction. All decent bike tires have good traction for commuting. Naturally, higher end tires have better ride quality.

2) Rolling resistance? Why? With a mid drive, its not going to make any difference at all to you. Seriously.

A thundeburt or Race King is a poor choice. Yeah, you can do it (I have), but realistically the cornering is going to suck – at the speeds you are riding its going to exacerbate the problem. Then there is the tread wear – with your bike that is going to be extreme. Off road tires wear out very fast when used for the application you are describing. They are going to be slicks in months (or weeks).

That is just my experience for your use case. Personally, I use a Serfas Drifter for your type of riding. Inverted tread, pretty tough and long lasting. I’ve tried a lot for your use case, but this is the most practical. Certainly, Schwalbe and Conti have some good e-bike rated tires.

Schwalbe has a line of e-bike tires.

1) Lots of long wearing tires tend to be pretty hard, and not necessarily confidence inspiring.

2) Rolling resistance. I ride mostly at lower assistance levels, and the current tires just have a lot of drag. Getting better tires would add 1-2 mph easily. The mid-drive is programmed to not launch hard, so it doesn't seem to be that hard on tires.

Realistically, I'm going to put about 3000mi on the tires every year. And I'm probably going to want to replace tires every 2-3 years, just due to age. That means a tire needs to last 6k-10k miles, which isn't that big a stretch for most tires. With that in mind, I'd much rather have a tire with better rolling resistance and traction over a high-mileage tire that's just going to age out.

Makes sense.

Short of a touring tire, I find most good tires are comfy at the right pressure. Shoot, going from 35mm to 50-60mm is going to give you a pretty comfy ride (at the right pressure).

As long as you are not bottoming out on the rim and the handling is not squirrelly, you can typically go lower with no ill effects. The inverted tread for me has worked well for a powered commuting tire. Schwalbe makes some great commuting tires that are fairly comfortable, great rolling resistance and fit well with commuting.

I cruise at 22-26mph, and that power, although not huge, takes a huge toll on knobby mountain bike tires that are designed for dirt. My motor is doing about 250 watts, and my leg are doing 250 watts (roughly). Tire wear is a lot like riding a tandem with my brother - tire life is probably about half what it would normally be.

And, cornering on a tire like the thunder burt is a lot, lot different than the tires you have been on (or anything with a rounded profile and minimum to no tread). Its not dangerous, but you can not really lean on it as hard is you can with a tire designed for pavement.

In my experience, my speed is not affected by the type of tire. I use race tires, commuting tires, mountain bike tires, even studded tires (which are horribly slow on a traditional bike). It does tend to affect range - on racing tires and a drop bar bike I can probably go 20% father if that makes a difference. Still, there shouldn't be a huge difference in range in the tires you are discussing.

Are silkworms that bad? You on the 120tpi version? Maxxis doesn't always make the most efficient tires - I wouldn't be surprised if Conti or Schwalbe rolled a lot better.

My mountain bike is on Schwalbe Hans Dampf and my road bike has Pro One (tubeless), so I'm used to riding on a variety of tires at pressures. I think the tires are a Maxxlite Speed, they feel pretty good as far as ride feel, but they don't seem to roll much faster than the HD's. The Pro One is an entirely different class of tire. I'm noticing that it's taking 75-100W to maintain the same speed as I can on the road bike. Some of that is certainly aero drag, but at lower speeds, it seems like there's probably 20-30W to be saved with tires.

The semi-tread feels about right. Most of the riding is pavement, but it's handy to have mild tread for taking short-cuts through gravel or dirt trails.
Something like a Speed King, or Terra Speed. The Schwalbe Hurricane looks interesting, as does the G-One (but until recently was only up to 40mm). I'm considering the Marathon Almotion for rolling resistance, but the review mentioned a very stiff casing so which negates some of the low rolling resistance advantage.

Well, the Terra Speeds will last about a month on an ebike on pavement. Thunder Burt certainly has low rolling resistance, and makes my bike handle like a truck, but in a straight line it has low rolling resistance. The G-one is a great do anything tire (well, not mud) that is a better all around tire than the Terra Speed - although the model they just released bombed in the latest rolling resistance test.

While I ride those tires, I haven't ridden the Marathon or Hurricane - they look like they would do the trick. Personally, I'm fine on a slick tire for commuting and gravel and grass. They don't drift very well (if you ever get into a slide) and can't claw their way out of a rut, but those aren't a priority when I'm commuting with gear. Jan Heine wrote an interesting article saying tread was about worthless for a bike tire (except for mud). I tend to agree to a large part - with the exceptions I just mentioned.

Schwalbe Big Apples or Schwalbe Big Bens. Commonly available in 29x2.0 to fit the Toughroad and tough. You can get really heavy ones with puncture protection bands--the hardcore pipe hitting Schwalbe greenguard bands--designed for ebike use.

Tires with smooth centers and knobs only on the outside have a very specific place in bike riding and that place is not around pavement paint. Many years ago I was funning kenda kwik cross or something like that for commuting and while I really liked them I finally switched to something very different after 3 sets of cycle cross tires. The widely spaced knobs on the shoulder would slip out every time on wet pavement stipes, usually in my condo parking lot or the one at work. After that happened several times I was paranoid of going down while turning on a cross walk in the rain and went to a rounded profile touring tire. Marathon plus I think, they have been on the bike so long I cant remember anymore. The current long tail Ive been riding came with a similar knock off tread and I've been pretty happy with that also.

Just something to think about depending on your route.

EDI: Just rereading the OP, minimal rain travel was something I missed the first time, my bad. Leaving up my original post for others.