Yeah, he can make another account, but it at least puts some stones in his way.
I mean, he could make a new account after getting perma restricted as well... or at least once he gets perma banned for feeding/trolling as so many others before him.
Besides, permabanned players are a tiny minority. If Riot's trying to make money off permabans, they have a terrible business model...
Especially since you would have to be a gigantic idiot to still give money to a business that essentially just told you to fuck off and take your money elsewhere.
Regarding the ranking system:
Read up on the law of big numbers. You are the only constant, thus you're the only thing not evening out over time.
The system might be impacted by others in the short run, but in the long run it's more accurate than anything you can think of that attempts to measure individual performance.
This has been pointed out and explained in great detail in so many threads.
Also, even if the system was inaccurate on a large scale (which again, it isn't), at least 50% would have to be on the lucky end, since it's a relative system. Are you really trying to say that every flamer, every troll, every intentional feeder is not only in the unlucky portion of players, but also created by being in that unlucky portion of players, rather than just being insensitive assholes?