In reply to Donnie:
One is always worst, but you can almost certainly more easily tell which ones aren't worst! In your example, if you were able to knock out 6 one armers whilst climbing Fr6c then pushing to 8 wouldn't help you improve anywhere near as much as focusing on something else - technique, fear etc.
For most people it's probably either fear/overgripping, speed, efficiency of route reading and movement, that sort of thing. Power to weight ratio is probably irrelevant if you never push yourself to falling for example. So improving power to weight would have a benefit, almost certainly, but putting the same effort in elsewhere would probably generate a greater benefit.