Some phones are very hard to read in bright sunlight.

Even if I could see my phone in bright sun, it uses up power much faster than my GPS. For bike touring where I might not have access to an outlet for several days at a time, I want to be able to charge all my devices from a dynohub and I doubt that I could do that if I tried to use a phone instead of a GPS. Most of my tours are remote enough that I might go for over a week without access to an outlet.

There's an energy cost for all the things you prefer about a phone - bigger, brighter, higher resolution screen, connectivity, etc. That cost can be mitigated by downloading maps and routes, using airplane mode, using Dark Mode (for OLED screens), and (the biggest battery drain of all) turning off the screen when you don't need it. The OSMand mapping app is supposed to do that automatically (working with your phone's energy saving mode) but I've never gotten it to work reliably.

On the last trip, I had the phone charging via a battery bank I stuffed in a feedbag. I just started researching rugged, weatherproof Android phones with large (10,000 mAh and more) batteries. I saw one that also had a large speaker - I enjoy some music once in a while - so I may try it out.

Whether or not this will work for you depends on how often you will have access to charging.

Garmin products are always discounted several times a year. They are currently discounted for Black Friday. The last time they were discounted was a summer sale at the beginning of July.

You don't have to wait 2 years.

Since I have only used general recreation GPS units, I do not know if or how to load alternative maps to a cycling GPS, or even if it is possible or not. In post number 4 above I listed two links for maps that I use for non-cycling GPS units. But one of them, I can't really explain how to get the maps from the site to my GPS, as I do not remember how I did it. But the BBB bike maps were pretty easy for me to load into my Garmin 64. NJKayaker knows how to use those sites, ask him if it works and how to.

The Edges use the same maps that your unit does.

Copy the “img” file to the \Garmin folder on the device.

The Edges need the “Latin” maps (Unicode doesn’t work).

The alternative maps aren’t really going to look better than the maps that come with the device. Though, people might prefer different looks.

The bbbike site is a good source (there are other good sources too). I like having the option to create custom versions (bbbike provides custom regions).

https://extract.bbbike.org/

Is the question here about loading a route onto an Edge device, or about changing the base map?
Loading a route is straightforward and supported by any of the Edge devices for the last ten years or so.
You export a .fit file from rwgps or whoever and copy it into the New Files folder on the Garmin device. Or else link the RideWithGps accounts with Garmin account and you just favorite the route on rwgps and over it goes.

I'm pretty happy with my Explore 2 purchased direct from Garmin. They were good to me and my running gps watches.

wrt the phone on the handle bar as a gps, mine does not work worth a darn in the rain or last very long and I only need the gps on long rides in unfamiliar territory.

I bought my Edge Explore 2 here in China and of course it came with Chinese maps. But I switched them to maps of Canada for a trip there this past summer, and Garmin didn't charge me anything for those maps - I was able to download and install them through Garmin Express for free (and back to the Chinese maps when I returned to China after my holiday too).

That was exactly what I did ..
Can't go wrong with Garmin.