I'm not trying to measure how big League of Legends is as a multiplayer game, as an esport or as merchandise-seller. I'm trying to get a handle on how valuable the name is when you slap it on a different product that competes for time in the same space.
Those restrictions are asking the question: Is the strength of the IP in the dressing or in the gameplay? Riot Games is making the bet that the LoL brand is transferable to other kinds of genres. If people have developed an attachement to the characters and world of Runeterra, the spin-off games will be successful. If League players are loyal to their particular style of MOBA above anything else, then the franchise will remain a singularly focused phenomenon.
The "What If?" we're playing here is "Does LoL lend itself to a diverse portfolio like Riot Games is attempting to build?" And for that sales power, public awareness or player engagement are unreliable indicators.
And my point is that the questions and point are absurd for various reasons. The strength of most IPs is not judged so harshly, and most tend to be a percentage as popular or long lasting as League of Legends.
But the other, more relevant reasoning is: the successes and failures of new IPs rarely happen so perfectly as to pinpoint perfect causes and effects. Does the League fighting game fail because it's associated with a weak IP or because it's not a great fighting game? Does it succeed because it's associated with League or because it's an easy to pick up fighter with esports money behind it?
These questions come off as arbitrary because there's no metric by which the answers can be judged because game releases aren't perfect.
And the ultimate point: League of Legends is a game that has existed for over a decade and is still absolutely massive. It has undergone significant core gameplay changes and through all of that, it has grown and cultivated a large dedicated audience. You don't go through 10 years of significant changes, some not so good, and still be a massive success unless your brand has goodwill and value. And that's not even taking into account added modes, that play little like a traditional MOBA. Not to mention the thirst from the community for spin off titles has existed for a long time, so it's not as if these announcements are for an unknown audience.
It has accomplished things that very few IPs in the history of gaming have and it has stayed relevant longer than most games have. At this point, it's not on League to prove its a big brand. Other games have to prove they are on a similar level to League.
And not only that, I would argue that the name "Riot Games" holds value and is a brand for millions of gamers, similar to prestigious studios. And that only gives the IP more value.