I've seen complaints that one person gets way too fed and the game is over and I also see complaints about how no matter how good someone does if they have a bad team they will lose. So, do you think the ability to get so fed you can single-handedly win the game is a healthy thing or should league require teamwork?
I think you should be able to carry via your rotations. For example, I play Rengar top a lot and get first blood quite a lot, and I try to zone them and hit 6 before them and then I ult mid or bot for 2 reasons.
More stacks = more AD
It gets the other lanes ahead
I think this is a fine way for me to carry, and I have carried some like this. Even if I go bruiser like 
and end with a score of 6/3 I still carried my team.
I don't think it's fine that as a fed Riven I'm able to 1v4 sometimes. More recently, why is it OK for a Vayne with 2 items and a score of 5-0 from killing TWO PEOPLE WHO SHOULD BE WORTH LESS GOLD EACH TIME be able to 1v5 at 15 minutes?
Who and why.
If a Pantheon gets fed out of the wazoo early game and can force the game to a close, yeah he deserves to solo carry. If the same said Pantheon gets fed...in the late game, not so much.
I mean it's entirely possible to carry or at least change the course of the game without being fed 
. Likewise, being fed is not always a free ticket to win. It requires context and specificity and making a blanket statement like "If you're fed x amount you win" is just hazardous for game health.
