It's really hard to have a group discussion about climbing on a forum, since everyone's definition is different. For some, a Cat 4 climb is significant. Others have small but steep hills. Around here we are lucky enough to have a variety of climbs including a 15 Hors Categorie climbs within cycling range. Because of that, we have a lot of cyclists that do nothing but climb all the time. These guys are strong and rail thin.
The fast climbers are probably doing around 15-20k a week and are around 2 pounds per inch of size and their 20 minute power output is probably around 4.5 w/kg. Many of us can't get to that weight (I can only get to 2.2) and getting that kind of power while staying thin takes more work than recreational riding. For me it means losing my upper body mass, which my wife is no bueno with.
So its a weight and power equilibrium. We have a 200 pounder here that is fast uphill because he has a massive FTP.