MIT may attract more people… but why would that be people who would contribute back in the direct you want? I’ve seen many MIT extentions for Godot, maybe they would have some insight.
Most indie devs make their MIT Godot games proprietary and I doubt peer pressure has ever stopped companies from taking MIT work and making it proprietary before. If software freedom of your users is important then the copyleft aspect is an important way to protect their freedom. Imo, not worth losing that on the off-chance it all goes well.