Let’s switch gears a bit and equate this with something else: Building a house.
Joe starts to build a small house to sell, but does not seem very good at it. At one point, a wall is starting to fall on him. Bob (who is a complete stranger, and about equal in skill), sees the danger Joe is in, and runs over to help, then decides to stay and help finish the job. Sue also comes by, and decides she could brush up on her hammering skills, so joins in.
At the end of the day, the house is built by the three complete strangers. Joe owns the house, as he started it, but Bob and Sue get a bunch of experience helping put it together. Now, you might think Joe is losing out on experience, as Bob and Sue did most of the work. But this is not the case, as he was able to watch the other two ply their skills, and learned from that. Next time he goes to build something, he will be better due to their help. Joe -could- be a nice guy, and offer up some of the money for the sale of the house, but that is his choice.
If Joe had up and vanished while the house was being built, then rights would now belong to Bob, followed by Sue if Bob did the same.
Now for some numbers:
If Joe had build the house entirely on his own, he would get 100% experience added to his house building skill, but it would have taken a lot more time.
With Bob helping, and doing half the work, Joe and Bob only get 50% base experience each, but get it twice as fast (and with less danger), plus, they would get a certain percent bonus for working together (as it is always easier to learn with more than one person doing a task). So each may get 60% of possible experience.
Now we get to Sue, who is very good at the skill, and does about the same amount of work as Joe and Bob put together. So, Sue gets 50% base experience, plus 10%ish extra for working with others. Joe and Bob both get 35% with the bonus. Plus, since Bob and Joe were working with someone who was better than them, they get a free training bonus without having to pay a teacher!
So, is this unfair to Joe, who loses about 65% experience on building the house, but gets to keep all the money if he wishes, and also gets free training (to be converted to actual skill when used)? Add into that how much faster the house was built.
Is it unfair to Bob, who gets 35% of the experience, plus the extra training just for stopping by to help out?
Is it unfair to Sue, who could have skipped the small house and built a mansion instead, based on her skills?
All in all, I think this would be a better way of doing things (but only if PP was shot, killed, and buried in a deep grave).