Those dubious features are so relevant to daily work that I didn't even knew they existed.
Instead Mercurial uses additional cache file which instead is slower on Linux with big repos. But happens to be faster in Windows.
And the octopus merge is used by kernel maintainers sometimes if not quite a lot. That feature is impossible to add in Mercurial as it does not allow more than two commit parents.
No it doesn't? People use octopus merges all the time, every single day.
To emphasize that even more: Try to explain the concept of an ML-style sum type (i.e. a discriminated union in F#) to someone who only knows languages with C++-based type systems. You'll have a hard time to even explain why this is a good idea, because they will try to map it to the features they know (i.e. enums and/or inheritance hierarchies), and fail to get the upsides.
Lacked a few dubious features such as merging multiple branches at the same time too.
It has improved but git is still noticeably more efficient with large repositories. (Almost straight comparison is any operation on Firefox repository vs its git port.)