To answer the original question: yes, I think Americans can really do comedy very well...
I loved the American silent comedy era... my favourites are that old silent stuff and Laurel & Hardy, Sgnt Bilko, I Love Lucy, Bewitched, Cheers, Frasier, The Simpsons, South Park, King of the Hill... any Woody Allen...
I did not like Friends very much as I found it just too schmaltzy/geeky... Golden Girls was too aspirational...
I have never seen Curb your enthusiam or Seinfeld so I don't know about them...
America is a funny country... except when they go to war... only country that's ever used a nuclear device in war and on helpless civilians (twice)... not funny... no sirree bob! goddamnit!