Developer productivity outside, I'm curious if garbage collection (which almost every functional programming language all have) would become an issue. Especially if you're making a 2D platformer, you really don't want to have any sort of frame stuttering.
And yeah, compile times are really a big problem if you're making games, because you need to constantly tweak your game logic and playtest). To be fair C++ also has this issue, but fortunately there are ways to alleviate this problem (minimize template usage, do not use libraries which use template metaprogramming like the notorious Eigen, divide your files into source/header files frequently, etc.)
Unless you’re making a large or complex game, I doubt it will matter. Remember that Minecraft was written in a garbage collected language (although its possible they carefully do object pooling, I’m not sure they did in the early days).
On your second point, some people dynamically recompile C++ too! I guess that code maybe is designed for fast compiling. Many other people use an embedded language like Lua for fast iterations.
And yeah, compile times are really a big problem if you're making games, because you need to constantly tweak your game logic and playtest). To be fair C++ also has this issue, but fortunately there are ways to alleviate this problem (minimize template usage, do not use libraries which use template metaprogramming like the notorious Eigen, divide your files into source/header files frequently, etc.)