> Part of it is because of the JIT runtime and a sub-par LSP (at least when I last tried)

Good LSPs do the autocompletion, sub par ones don't.

Is it really such a good idea to have every single automated aid turned on when picking up a new language?

How will you learn if you cannot get feedback on what you did wrong?

I mean, until you learn multiplication, maybe don't use the calculator.

Once you learn it then you get a small speed increase, but if you are new to something, LSP autocompletion is going to slow down your learning.