Curious - is your team using GDScript, C#, or C++ primarily? It seems like GDScript is still the happy path for compatibility, but I have mixed feelings about it as a language (though I've written enough Python to be relatively productive in it in my little Godot experiments).
We're using GDScript and like it a lot. I find that I'm much faster than with C# and haven't had any performance issues yet. The good thing is that you can mix and match languages as you like. So you could write 99% in GDScript and there's something where you really need performance just write it in C++, Rust, Python or any other language you want.
It looks like that they're re-working GDScript for 4.0, so that'll get a lot better, too.
I've used Unity and Unreal Engine 4 for a while I don't think i'll want to switch from UE4 for 3D based things i'm pretty excited for Godot 4.0 and all the new nifty features I've been hearing about.
Does it make sense to hold off diving into Godot until 4.0 (for 2D-based things) or will there not be too much to "relearn"?
I'm not a contributor to Godot, but my understanding is that Godot 3.x projects will be mostly compatible with Godot 4.0, and where conversion is needed they will provide tools.
Therefore, I assume that the fundamentals of Godot will stay the same and you should be fine diving in with 3.0 already :-)
I've switched from Unity ~7 months ago and never looked back.