There's plenty of other reasons the colleges are bad but his argument is a holistic one and so trying to break it down to constituent parts loses the greater picture, for what it's worth theres a fair amount to suggest that ultimately the elves did half ass teaching the humans in the end mostly because they were rushed but also because they were pretty arrogant and thought humans weren't really capable of much. The fact that examples like Fozzrik exist suggest that humans ultimately are more capable than given credit for and one of the bigger issues with the colleges is that it promotes stagnancy. The monofocus winds of magic is undoubtedly safer but it does mean that exceptional human wizards are going to be trapped in one wind and you'll never get human mage equivalents to Sigmar ever again.
Well, to be fair Fozzrik might have been a renegade sea/high/wood elf mage running around the Old World Asarnil-style. I don't think there's anything that says that he was a human. Other sources we have say that it's literally impossible for the human mind to cast high magic because it can't hold eight distinct and in some cases contradictory trains of thought and emotional states simultaneously in the way an elven mind can. Him being human does have a lot of unanswered questions, such as who taught him and where.
Wind monofocus has enabled humans to do things that elves can't do/haven't been interested in. Chamon based magical alchemy is something that the elves never came up with. I think the various ascension processes are similar. I think that no high elf is as good with Shyish as Elsbeth Von Draken, and she's less than two centuries old. The Colleges are also continuously researching and extending their knowledge. They're dynamic institutions, as shown by Mathilde's patriarch being a magical research specialist. In some ways they're lucky that the elves taught them the basic principles and then left them to develop it themselves. It's forced them to be innovative rather than stagnant.