I am really big on improvisation, and I really can't see how a 3D VTT can accomodate that playstyle. I feel like it'd force every DM to be a level designer, and I feel like that's one step too far. Even Foundry VTT feels a bit too much sometimes with dynamic lighting (which requires me to put walls, light sources, doors, windows etc.) and automation (automating spells so they immediately ask for saves, associating specific animations with specific spells, making it so casting a summon spell immediately creates a token for the desired creature etc.), and that's only a 2D VTT. I can't imagine needing to do the same with a 3D VTT.