I have a dumb, wheel on trainer (Kinetic Road Machine). It transmits estimated power data via BT, which is pretty darn close to my Stages crank PM. You absolutely can get fitter on a dumb trainer, but the key is intensity and consistency. I do both TrainerRoad and Zwift (often simultaneously: TR for the structured workout and Zwift for distraction). That said, all my friends who have gone to a direct drive smart trainer say that the experience is more immersive and therefore less boring. Plus, it's just super efficient to have the bike on the trainer and all ready to go on a cold and wet winter morning before work. Since we may actually have a wet winter here this year, I'm going to be asking Santa for a Wahoo Kickr or Elite Suito.