Becoming overpowered is kind of the end goal of the game.
I don't see this at all. But I do agree that at some point you should be able to use your dragon souls towards a perk. Otherwise they just build up and up. I'm sure I could only absorb so many souls.. I think.
And to the original point. I don't want to be trading souls like they're game cards. That seems kind of silly unless there was some way to cast a spell to pass it into a gem first. Otherwise it just seems like I'd be walking up to a greybeard and passing gas, hoping he catches it and absorbs it in.