I think this is only partly true. The other big benefit of monads is that they can automatically work with syntactic-sugar such as do-notation to allow non-lin

I think this is only partly true. The other big benefit of monads is that they can automatically work with syntactic-sugar such as do-notation to allow non-linear code to be written in a linear way. Monads and syntax, even without HKT, allow the user to write their own async-await, option, result, list, etc. expressions.