Why do people only want mythology episodes? I like breather episodes, as they can take a break from what is sometimes tedious. Too much mythology just builds with no payoff. Remember Lost and Heroes? Those shows are proof that that does not work.
Just in case this was in part directed at my post: I don't want only mythology episodes. Mentioning the William Bell mini-arc and how it didn't bring the heroes any help with the mythology was mainly because the series has presented Bell as a guy who may have all these answers that Walter doesn't. The recent arc deflates the idea that he'd have any ideas on how to solve this problem.
But I don't think Lost and Heroes are "proof" that all-mythology shows can't work, just that those two didn't (for me).