Care to give examples? I know that the language isn't fast, but afaik nearly all shells are interpreted. There have been performance problems with break/continue in earlier versions as they were implemented using exceptions internally. But that doesn't really qualify as "basic commands", I guess. Cmdlets should be not much slower than running the equivalent C# code yourself.
Hmm, I can't seem to reproduce many such issues with this machine, except Get-Help the first time I tried it. I think it could be that the cmdlets are only slow on the first run (enough to leave me with a bad experience), or the SSD on my PC masks the problem. It's good to know that it's not always super slow.
If it's slow on the first run, then it might be loading a large interpreter from disk. If so, MS might have let the interpreter get a bit ungainly -- you might argue.