I've been doing Zwift for awhile using the PM (and a BT bridge heartrate monitor) on a dumb trainer. I've never used a smart trainer so I don't know what I"m missing, but I don't think it's much. I actually was in the market for a new trainer this year and came very close to buying a direct drive trainer, but what killed the deal for me was that most of the time I'll use the trainer to warm up for races and I didn't want something that I had to plug in.
So I got a Kinetic Road Machine. It calculates your wattage based on drum speed and a power curve. Compared to my Quarq, it runs about 5% high and has a bit of a lag so it doesn't respond immediately to short, sharp efforts. But it means that I can do Zwift with any of my other bikes without a PM.
Also if you're mostly using Zwift in workout mode, you really don't care what other riders are doing so getting dropped when there's a surge isn't that big of a deal.