Parmandur
Book-Friend, he/him
WotC producing loads of quality art assets in a timely manner is, like, their core competence as a company: look at Magic, and more relevant lyrics, what they do for Arena on a constantly releasing basis now.There is some really great D&D terrain available for tabletop simulator. The official VTT stuff will probably be prettier, but it will take years for them to get a big library -- unless they partner with someone like Dwarven Forge, and then you are talking about a pretty big expense or (more likely) multiple subscriptions (one to the VTT, one to DF, one to Hero Forge, etc...)
I'm sure there is some great stuff for Tabletop Simulator, but there is for Magic as well and that's just not the same thing as Arena. Too much hobbyist set-up work, which is why I say there is nothing quite like what WotC VTT is looking to turn into: a high-quality, easy to use and casual 3D tabletop simulator.