This gives the false impression that xmonad is not as fast as other twms. Xmonad is very lightweight, the package is below 500kb, which is below i3 and awesome. It has a very minimal and clean interface. The configuration file IS the twm (similar to DWM) xmonad is just a library. You write your WM which might be a turnoff for users that don't want to spend the time doing so.
Since xmonad is a Haskell library, you need the compiler. There's a reason why ghc is so big compared to other compilers, but just because it is a big dependency, it doesn't make xmonad any less lightweight
Yes, it only a really major inconvenient if you have very very limited HD space, which is a rare thing these days. And you can always uninstall ghc after configuring xmonad.
Since xmonad is a Haskell library, you need the compiler. There's a reason why ghc is so big compared to other compilers, but just because it is a big dependency, it doesn't make xmonad any less lightweight