It's a difficult decision to open-source something you've worked very hard on and could very well make it much easier for competitors to destroy your moat. I wonder if anyone would support such an open-source framework financially.

I understand that sentiment. You recreated diep.io so obviously their moat wasn't wide enough. Is the moat of having a Canvas renderer enough to prevent someone from making another diep.io game? Or does making any game from that renderer naturally compete with your game?

AGPL might make sense with dual licensing so that any potential commercial competitors who use your library have to give you a vig, but anyone willing to use a compatible free license can use your code.