I can't recall Dennisson ever lining up a squad that didn't require run game establishment to succeed. Even the playaction boots use identical zone run blocking to the runs. Or at least they did in '10-'13 in Houston.
And I'm skeptical that a lack of deep threat is THE problem as everyone is clamoring. From his days in Houston, think Arian foster, Matt Schaub, this brand of WCO is about moving chains, short stuff, 4YPC, digs and slants. I don't think they are dialing up that play.
Like a few prescient posters suggested, this may simply be a poor fit for Tyrod, who worked better from the pistol formation and shotgun. When the o line and run game can't get going, they need to switch it up.
I have posted this several times - I do not expect them to try and fit the offense to TT at all. He is a bridge to the next guy.
They are building their offense for the coming years and TT is not a part of that plan.
They were looking to bring in WCO slot WRs that can run a bunch of routes from all over the field. They are looking for RBs, FBs, and TEs that can run a and catch so they can utilize the entire width of the field. It is a very horizontal concept with multiple levels where you need your QB to read one guy and decide between 2 routes. This is not a fit for TT, but hopefully tells you what they are looking for in their next QB.
If they wanted to build for TT - the offense and the players need to be very different. Rex and Roman (& Lynn) were using TT as the QB of the future so they designed an offense to fit him.
I believe Dennison could build plays that better fit TT, but that destroys what they want. McD has repeatedly said they are building a team. They have a offense they want and are going to run it to try and determine who fits and who doesn't as they move forward. I think about 1/2 way through the season they will change QBs and we will see what looks like a totally different offense with a more rhythm passer.
I think they are trying to win with TT - a safe QB- but they do not want to build around him so they are trying to fit him into the concept they want run.