That thing can be discussed. What about demo or free money then? They also give chance to test any game on a platform. They even give more chances to test any game. Lets take BetFury for example - you get 42 sat hourly. Minimum bet is 1 sat in casual games, slots usually ask 1 cent for a spin, which is more than 1 sat, and blackjack ask 10 cents for example. So I would not call faucet as something you use to test games. It is more like a way to hold customers imho.
I agree with you that demo money would be optimal with that but sadly you can't use demo currency with in-house games. Also sports betting doesn't accept demo money so you cannot try all the unfamiliar nuances of betting in there. That would be a sweet option to have to test out some specific betting i've never even tried.
His example pertains the Betfury free sats every which you can use on there house game while slots has demo games to try it. I believe live games is the only games that missing the experience for not depositing real money since there minimum but is high enough for the faucet amount.
Besides your example for sports betting as demo is really not necessary. No one wants a trial bet to experience sports betting because the sports game will play with or without your bets and you can experience it by just watching it and make an assumption bet compared to casino games that you need to play for the result. This is my first time to here a demo on sportsbook.