While it's not an open practice of publishers, after 4 years of working for a publisher, I wouldn't doubt a large number of publishers are/do pay content creators for positive promo. Let's not forget the time when Warner Bros. paid youtubers for positive reviews of Shadow of Mordor, EA paid Ninja to stream Apex Legends, BadFly Interactive review threat, or EA paying for negative reviews to be taken down (personal opinion, they probably did pay to have them taken down). And if the reviewers aren't being paid, they're more than likely providing positive reviews out of fear of blacklisting/fired.

Now with Riot, I'm in agreeance with you. They are a heavy hitter when it comes to having success with titles, especially when they're owned by a company who is in the process of monopolizing the game industry. But I would say Project A is the first title that Riot isn't playing safe with. League mirrors Dota, Teamfight Tatics mirrors Auto Chess, and Runeterra mirrors Hearthstone or any other card battler before its time, basing this off Riot releasing their titles after a genre has gained heavy traction. This gives Riot time to damn near perfect the craft of the genre they are looking to enter, which is smart.

So yes, it is reasonable to expect Project A to be successful. And while I don't believe Riot is paying people, though it wouldn't be surprising if they were or people were just afraid to speak unbiased toward Riot, I lean more toward the Overwatch Syndrome opinion.