[coolplants]

In my experience that has not been the case. Either unacceptably slow computation or High memory usage.

[whateveracct]

I mean, what use-case was this?

I've deployed plenty of web services & data processing jobs in Haskell and the RTS has never been a bottleneck or issue. So I'm guessing you weren't doing an IO-bound activity (where Haskell is quite good.)