Stadia isn’t being held back by current gen, game performance is about the same on Stadia as Xbox One X for the majority of games. The specs for next gen consoles are also seemingly superior to Stadia in its current form but the advantage of Stadia is they can upgrade the specs without the need for new hardware.

What’s holding Stadia back at the minute is it’s newness, devs are unfamiliar with development for it and consumer interest is still too small for devs to invest the same way they would PlayStation or Xbox. I’d expect these to resolve over time, as more people get on board with Base tier and the platform becomes more viable to invest in.