No "casual" gamer waits 5+ years LOL. Are you on drugs? Casual gamers are the ones consuming new media at its freshest. Casual doesn't mean occasional. There's a reason games like Madden sell like hotcakes every single year, it captures the casual audience. A more invested gamer would be more likely to research previous titles or market pricing trends. A more invested gamer is the one more likely to research older games to play and if it's worth getting the new one (because with Sports games, it never is).
You're not a "casual" gamer. You're cheap. Big difference.
$15 is fantastic. Absolutely fantastic. Someone sees $80 (in Canada, $60 USD), and might be taken aback. But $15? Fuck that's easy. Thats an hour or two of work for most people. People just keep subscribed to the service and let it run. They constantly get new games to play without huge bills attached. Win/win. It also more easily exposes casual gamers to older games thanks to the simplicity of the catalog and having every game at your fingertips.
And of course for invested gamers, the benefits are great. Want Watch Dogs 3 but know you'll beat it in a week? Buy a month of uplay+ for $15, beat it, unsub. It means a lot of people won't outright buy the game, but it also means cheapasses hyped for the game who weren't going to buy it (and more likely to buy it used) will spend the $15 to play it.
Like I said. It's a win/win for consumers and the company. It's an incredibly good tactic.
Also in regards to rentals, I paid like $10 for a week long rental. I don't give half a shit if this is just subscribing to a single publisher. A single publisher like Ubisoft or EA has a HUGE catalog of games for the price. 1000% better than rentals ever were.