Hightower looks old and slow. Until (unless?) he rebounds, the front 7 is a disaster. Relying on a 3rd rounder who missed his whole rookie year and can't even get into the active 47, an UDFA who also missed his whole rookie year, a castoff coming off a mediocre year from an awful team and a 5th round pick to improve is a stretch
Its not like they packed in 2-4 high end or long time proven commodities. It's a unit lacking high end skill or (in the case of Shelton and Clayborn) inconsistent and/of mediocre levels of play. There's no reason to think the unit will "come together".
DE who can't beat their man one on one is a talent issue not a cohesion issue. A DT pushed backwards routinely isn't a cohesion issue. A rusher who runs past the QB and plays with terrible awareness/discipline is not a cohesion problem. Having a group of holdovers (Van Noy, Brown, Wise, Butler, Guy) who max out at "serviceable stop gap role player" talent levels is not a cohesion issue
Will playing together make them better? Maybe. It didn't really help the front 7 last year with many of the same guys. A lot of their problem is a lack of talent. Coaches dress it up as "failure to execute". You know what guys who fail to execute regularly are? Players who aren't good enough.