It's really really hard to make a successful multiplayer CCG. I only know of two that did it well: Vampire: The Eternal Struggle and Babylon 5.
Oracle of the Void #Multiplayer
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y'know... I know Commander is more popular than other ways of playing Magic these days, but I don't actually know if Commander today is more popular than other formats were before Commander took hold, like, in 2012 or so.
It wasnt. It gained a lot more popular in 2016ish I think, but l5r could beat wotc if it had a stronger casual presence.
I think there's a litany of additional "if it..."s that you're leaving out of that statement in order for it to be true, chief among them being "...wasn't dead".
I would believe L5R could have beaten WotC if it had a better casual presence in 2011. By now, the only way it'll actually beat it is if FFG decides to do something else with it. Without the backing of a lot of money that can only really happen from a corporation, I don't think it'll go that far.
And... honestly, I think the game is really well suited to 1v1 games, and just not well suited to multiplayer. That's why there were so many attempts to make multiplayer happen that weren't just the standard multiplayer rules.