> Also a good spin bike does a better job at keeping momentum
With smart trainers this is no longer a thing. They can more reliably control the resistance to mimic the elevation percentage and rolling stop/downhill feel. If you are serious in anyway about riding there is no reason to not have a smart trainer at this point.
Kickr/Tacx/etc + $600-800 road bike + Zwift and you have comparable experience. Sure you wont get the human in your face thing, but a lot of communities on Zwift are embracing voice chat to communicate during the rides. Combine this with a much more realistic feeling to riding and it's pretty hard to beat. Thankfully some more companies are beginning to show up to try and make Zwift get better (like RoadGrandTour).
With smart trainers this is no longer a thing. They can more reliably control the resistance to mimic the elevation percentage and rolling stop/downhill feel. If you are serious in anyway about riding there is no reason to not have a smart trainer at this point.