Not a sailor of any particular ship but some thoughts:
Leonard and Sheldon are the key relationship in the show for me. The others revolve around them still, just less so than in the beginning. There have been a couple of times the writers have suggested Leonard is the key character of that relationship for me most notably with the ellipsis when Leonard goes to the North Sea...the show, literally, can't continue without him.
On Penny, she starts out by wanting hunky boyfriends but in her new world it transpires that as well as being hot she is the hunk of the show - the one that'll get 'all