How is it irrelevant? The issue was whether or not Leonard was a dumbass, not whether Leonard was better than Penny at making friends. Having a circle of friends is a good thing, and Leonard has achieved this. Whether or not anyone else has achieved it doesn't detract from Leonard's accomplishment.

"Having a successful career and being ok with your family - and even having friends - doesn't mean you can't be a dumbass."

This is true, but it doesn't address the point that these are all worthy accomplishments for a supposed dumbass to have. They're things a lot of people wish they had, so your argument's a bit weaksauce there.