LoL might be technically older than SC2, but surely you would agree that SC2's heyday came a long time before LoL's, yes? My point isn't to compare them and say one is better than the other, but to say that SC2 is further along than LoL on the same curve. In other word's, LoL's future probably isn't "bigger than soccer" nor "totally dead", it's "chugging along with a small steady player base and a few hundred people playing it professionally, but not filling arenas", which is where SC2 has been for 5+ years.
edit: as for investment, I think Blizzard's "sponsorship" amounts to letting them use the logo. Certainly they're not paying for things like professional caster studios and advertising, like Riot does.