Re: maturity - I think it is the latter where the problem is very complex and the dev time reflects that, it takes a long time to implement all the features people need and are used to in X11 (or, used to when coming from windows/macOS). For instance, screensharing is still not widely solved across all wayland compositors. In Gnome or KDE Plasma, it works as you’d expect. But a smaller project like river (tiling window manager that I daily drive rn) does not handle screensharing out of the box and takes some extra configuration - and even then it’s got some oddities that I didnt have in KDE.
As for your issues with NVIDIA gpus under Wayland, yes I think it comes down to driver support from NVIDIA (or the open source drivers just need to mature some more)