From my experience ProseMirror is not the easiest editor to get started with, but it gives you a lot of power in terms of customization and flexibility. Recently a more feature rich table module was released, which might come closer to what you expect in case you haven't seen it yet: https://github.com/prosemirror/prosemirror-tables. Once you get the hang of it, implementing custom plugins and behaviors is not that hard. There will be a 1.0 release with more extensive documentation soon, which will make it a lot easier to get started. You can find more information here: https://discuss.prosemirror.net/t/planning-new-documentation.

Apart from that, the maintainer is very responsive and often times issues get fixed in a matter of hours! And the community behind ProseMirror is very helpful and seems to be steadily growing :)