He was told his case was legitimate, but the cost was too much for him to afford. Also, large corporations have massive legal teams.

The narrative that is widely believed is that "the cost of making an accusation is so high that nobody would do it, so automatically believe accusers" and they pretend that there is no cost to being accused.

It's an oversimplification and ignores the game theory involved in these things.

Yes clearly, if he has corroborating evidence. Also, it's easy to get an unfair dismissal lawyer on compensation share I.e. they take 40% of any compensation as their fee. Plus if it's a major corp and your brother has evidence then they'll usually have a budget/insurance for paying off these types of claims.