Okay first off hardcore gamers don't run to the hardest game to master. If that were true Darkstalkers and Samurai Shodown would have had a lot more of the hardcore audience. KOF XIII gives the hardcore audience the game with the blend of accessibility and difficulty that they wanted. 3rd Strike wasn't that hard to pick up IMO, but had a lot to master and the more people played the more they got into it. XIII has that feel. Does it mean it's a lock to be a game with a long life... no. But it does have a good chance.
Second, 02UM is not really hard at all. If you are talking about the MAX combos compared to HD sure, but mistakes are easily more forgiving. I have not seen a lot of players stringing off touch of death combos on it easily. Are they there? Probably, but not too common.
Third I like Guilty Gear, but the audience on it has never been that big. Decent, yes, but not huge. Back in the xbox 180 days I could easily find games in any KOF game easier then GGXX, and GGXX was $20. KOF games were at least double the price. So, no a game with more incarnations then SFII is probably not going to be the answer to the hardcore gamers.