I mean I don't know anything about novel writing on tapas, but one of the big, big reasons I posted my comic here vs like...tumblr, is because Tapas encourages original works. You can get views here for doing your own thing.
Any other website I am on pretty much forces me to do fan content to engage with the community and make a following, and I like making fanart--but it has turned into an obligation. It used to be a fun creative place to experiment--it isn't that anymore. It's work.
But whether fandoms change the Tapas vibe would depend on if A03 or Wattpad suddenly became a lot worser than Tapas for uploading novels. The fic writers over there have huge libraries of their old stuff and probably have no reason to move. And, right now with how weird it is to upload pictures into text posts here on Tapas, I think you're safe of them jumping ship from A03.