> Haskell code can be optimised to run very fast indeed, but resulting optimised code does not look much like idiomatic Haskell at all.

It's still Haskell though, which means it can compose nicely with all that idiomatic Haskell!

Further I'd argue that you typically don't have to go to that level of optimisation.

I'd be very confident in my above statement replacing node or Python REST apis at least, but can imagine that not holding true in other domains.

In that case though, my first point still holds and I find that advantage very powerful.