Mazi Smith didn't flop because he was only 300 lbs or 310 or whatever it was at the end of the year. If he did lose 30+ lbs, it's possible he was weakened, having a big guy do that purposely in season is impossibly foolish, if it were intentional. Regardless, Mazi flopped because, among other things, he's the slowest player off the snap in the history of football. There were instances you can slow down the video at the snap, and after every player on the field has moved....Mazi is still in his stance.
Make excuses for Mazi, Jones, whoever, there are no legit excuses. Jerry Jones & co have no idea how to construct a complete roster. 28 years makes any argument to the contrary laughable. Mazi shouldn't be expected to contribute? Fine, what about other 1 techs they've drafted and developed who can play instead of him? Exactly, there are none. Most of their DT picks have been hot garbage. Their solution to fixing DT the last few years is trade a low round pick for a Raiders castoff, a guy who was a street free agent this past offseason, no one offered him, so they picked him back up for basically the league minimum.
They don't know how to find or make tough players. The playoff record since the mid-90s can't lie, it is what it is. That won't change until the organization does.