Might be a nitpick, but there’s also the problem of what exactly we are calling a “serious commercial project”.

Right now the most successful game made with Godot Engine is Cruelty Squad (https://store.steampowered.com/app/1388770/Cruelty_Squad/). Regardless of if you would call it “professional” or not, it was one of the most noted indie games of 2021, had great reviews, and probably was much more commercially successful than your average Unity/Unreal “professional” indie title (given how so many of them flop). Same goes for some highly successful RPG Maker games, which usually people would not call it a “commercial-quality” engine.

I think there’s a lesson here: don’t care that much if you’re using a “commercial” quality engine or not, just care if the engine will give the right tools to make the game that you envision.