Comparing Mixtapes and Transit seems a little weird if you ask me. Mixtapes's very nature of a band doesn't actually create any expectations. Their songs are almost supposed to be somewhat average -- but that helps contribute to the "hey these guys are just like you and me" that makes the band awesome. The new song doesn't help push any new musical boundaries, but Mixtapes aren't boundary pushers to begin with.
Meanwhile, Transit did create some expectations with L&F and then were victimized by their own success on Young New England. I know they can do better, so I expect better.
I think saying their songs are supposed to be "somewhat average" is selling the band short. By a long-shot. To a certain extent, I get what I think you're trying to say -- The songs aren't complicated. But ultimately, I think for a band to be succesful playing music like this ("pop-punk" for lack of a better term) there needs to be a certain level of songwriting. From my perspective, that's the band's strong suit. The lyrics, the hooks, etc. They aren't trying to bowl everybody over with insane guitar solos but...They do have a strong tendency to write catchy-ass pop songs that are relatable to a wide breadth of individuals while including fairly specific details that create a storytelling vibe.
I have expectations for this band. High ones. They just don't relate to crazy drum fills or fret work, y'know?