.NET has always had slow exception handling because it tied/ties in Windows’ Structured Exception Handling (SEH); that’s rather slow but provides e.g. detailed stack traces even for mixed-mode callstacks.

Having ported some decently large codebases from OCaml to F#, the heavy use of exceptions in OCaml (where exceptions are very lightweight by design) had to be changed to normal control flow with monads to achieve good performance in F# — specifically because of .NET’s slow exception handling.