Update: Riot have poured cold water on DFC's somewhat dubious report, asserting that they see over 500,000 concurrent LoL players in the US and Europe alone (as opposed to Dota 2's 300,000 odd globally). Riot tell me that DFC "is in the process of pulling their press release promoting this report." So LoL very much remains king of MOBA castle, whichever angle you look at it from.
An invite-only sequel to a free Warcraft mod is how the West was won. That's the claim, anyway, but so long as Valve keeps its internal figures locked up there's no entirely reliable way of knowing exactly who's playing what in PC-land. League of Legends has, of late, been hailed the most-played PC game in the the Western World, but the DFC Intelligence PC Game Meter (via GamesIndustry) has used assorted surveys (primarily of Xfire's apparent 23m users) and magick to determine that Valve's Dota 2 has now overtaken it. A victory for Valve - except LoL is actually far, far bigger than that.
Today's report doesn't seem to gel with LoL dev Riot's recent claim to have over 5m concurrent players globally, as opposed to what Steam's own graphs suggest (and recently averaged by a Reddit user) is a peak of 300,000 for Dota 2.
The discrepancy is because both of those are global figures - LoL appears to have much more take-up in the East than Dota 2 does. If DFC's estimates are correct however, Dota 2 is now top dog in this side of the planet. Which is impressive for a game that's technically still in beta (or at least 'early access), but ultimately pales into something like insignificance compared to LoL's global standing. The Riot MOBA's concurrent user count even outdoes the total Steam concurrent usercount (which hovers around 4.9m) by a nose. I'm a bit scared.
DFC also say that both Dota 2 and LoL are now way ahead of one-time king of PC, World of Warcraft. Bring on Blizzard All-Stars, I guess, and we'll see which way this particular cookie will crumble next.