Switching Forums to use Discourse?

[ryo]

I don't think disabling JavaScript is a very common use-case, but okay.

Admitted, it's not common indeed.
However, if you own an old PC where current year web (aka, web apps overtly bloated with Javascript) lags while normal websites work perfectly fine or if you take privacy very seriously, it's pretty essential to disable Javascript, or at the very least control it with uMatrix (so you can enable/disable specific types of elements for each individual website).

MyBB's editor simply does not work for normal formatting and it's even worse on mobile.

That's true.
I've never been a fan of WYSIWYG editors, so I just use it in "view source" mode (the right-most button on the editor that looks like a sheet of paper), which is the only mode that works without Javascript anyway.
Markdowns in Discourse is indeed 1 thing that makes it better.