Or it turns out B was wrong, willfully so, and A just lost their income. Sadly, this was A's most popular content and, since A was living paycheck to paycheck, they were unable to pay their rent and were evicted.
B went on to do the same to many other small content creators, because B has 100 million dollars in the bank.
Then A disputes the claim a YouTube asks B if the they are sure its infringing on their copyright. B lies and says yes, then YouTube sides with B while A gets a copyright strike, 3 of which and you lose your channel.
Scammers are also extorting money from Youtubers using this feature of Youtube's claim process. See: ObbyRaidz
In case of conflict, YouTube shouldn't blindly side with the most powerful party as they're currently doing. Legally the fairest way would be an impartial judge, but in practice small players can't afford the legal representation for that.
Yeah, there does need to be a way to restrict bad actors. And this is already a real problem: major corporations claiming copyright over other people's original content on YouTube, and that original content getting blocked as a result. When a company does that regularly, submits too many false positives, their ability to claim ownership should be restricted somehow. At least there should be some sort of reasonable consequence. But at the very least, the original owner should retain ownership and eventually get their money again, and that's not currently happening.
B went on to do the same to many other small content creators, because B has 100 million dollars in the bank.