It's been a year since Tape Deck Heart (and all the songs on the album were written well before that). I don't think it's out of the question to write 12-18 good to great songs in a year and a half+. He's also a solo artist (yes he has the Sleeping Souls, but he is the main writer). I say keep'em coming. Some artists don't require lots of time between writing like Brian Fallon, Dustin Kensrue, Kevin Devine, Andy Hull for example. There a lot who can like Frank and for multiple projects. Then you have guys like Brand New.
yeah, i understand your point to an extent. it just seems like each album has gotten progressively not as good as the last one over the last 6 years or so. as for the other artists you mentioned, i wouldnt say each album theyve put out has been renowned. but i also havent been a fan of the gaslight anthem in like, 7 years. all of thrice's stuff is good, dustins solo and new stuff, not so much. the only artist i can think of off the top of my head who is a machine that has a near flawless canon is trent reznor and even he has his missteps.