> no provision for clawback

Unless you're planning on quitting jobs mid year every year I wouldn't really call that an advantage. On all other years you either end up buying piles of shit you don't need just to not lose your FSA dollars you gambled that you would use but didn't, or end up underestimating your medical bills. It's such a broken system that one even has to make guesses like this. There is no need to make people guess.

> funds being available on day 1

Most people with FSAs have higher disposable income so this isn't really an advantage either. Lower income folks typically have HSAs instead.