IMO I’d rather just write idiomatic C++ then non-idiomatic ghc-specific Haskell code if performance is important, and it nearly always is.
And idiomatic Haskell's performance is plenty acceptable for a variety of common use-cases (so not "nearly always is")
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.)