> The engine is slow

doesn't really seem that slow for me (but of course, i haven't used it in anger yet).

> the editor is buggy, the language (GDScript) doesn't have the features of a modern scripting language.

the editor is enough for small scripts, but you can also choose to use your own native editor, or switch to the C# version (and use visual studio or jetbrain rider).

I don't find the scripting language any worse or better than any modern script languages. What are the missing features?