@Lord Magic - I think that performing cardistry with magic gives the audience the easy explanation of "skill" and showing off. It then puts your magic in that same context - a performance of skill or a look at what I can do.
If you look at
@Jason England's card handling it isn't show-offish, but has an elegant precision. He comes across as someone who knows what he is doing. Same with Roberto Giobbi. You know they have mastered their craft, but there is nothing that unnecessarily draws their attention to the way they handle their cards. It is like a magician having confidence but not coming across as cocky.
Exactly.
The play there is that it looks like a mistake as opposed to ineptitude. If you oversell the ineptitude the audience either doesn't believe it or actually believes it -- neither is a good result.
Lennart has a great character. However, having seen him perform live, it becomes a bit tiresome and implausible. The first effect, it is unexpected and amazing, the second effect is expected but still amazing because you were watching his chaos with cards more closely, the third and subsequent effects become just more of the same. At some point, his schtick overwhelms the effects because all of the effects start looking the same. Also, I'm pretty sure it isn't a joke.