Hearthstone is a unique bird as its playerbase is used to Blizzard and Magic and so expects to pay something like a AAA game price for card unlocks. It's not really necessary for Blizzard to sell the idea of paying in Hearthstone.

Clash Royale is very aggressive about getting money. It does appear passive because it's better for revenue if non-enthusiastic players progress slowly, but trying to do anything but play a few games a day without spending money is intentionally made difficult as you'll run into progress blocks faster that way. It's quite clever. It also benefits from increased sophistication of players in that it can signal when to make the premium purchases more subtly than was necessary a few years ago.

I haven't played Assassin's Creed, but it makes sense to me that a AAA game franchise has a better chance standing out on mobile as a premium game, rather than associating with less prestigious IP. I certainly think Ubi has learned from its poor attempts to milk its lower-priority IP by farming it out to F2P developers, so a transition has been made in the company overall.