I think the real use case for FSAs is people who have regular or predictable health care costs. If you know that, every month, you need $500 for insulin, or every year you have two $200 dentist visits that aren’t covered by insurance, then paying those expenses with pre-tax money can be a big savings - saves federal tax, payroll tax, and state tax. If you’re a young, healthy person whose biggest health expense is hangover advil, then FSA is not for you.
The vlogger’s problem is he was putting money into the FSA “just in case,” and got screwed because he didn’t have need. I’m sure there are tons of HR departments out there that do a terrible job of explaining the use-it-or-lose-it nature of FSAs, so it’s valuable to have the rant out there, but they are good accounts for the people that benefit.