I would start to ask:What has Palmer to work with?
I think that the Gm has done quiet a good job to put this team together.
I believe that you can add some FA to an existent core of players, use an established system, and after that process is done, then any team in the league can skyrocket.
Imo the Texans don't have established their system and still need some players to complete the core unit. Some hangovers from the Expansion draft were used to fill in but aren't the best fit. You can do better and maximize your output by that. So i think, they hit the acheivable limit for this year. They have the potential to go up, but Stability isn't there. But the Texans have more stability than last year.
Saying that i doubt that Palmer could do better. The staff makes game plans, prepares the player and tries to realise that the mindset of all 53 members is focused and right.
If Palmer would have benched your best OL and because of that DD and Carr have no time and lanes, alright. Then go and question him, but with that Oline Material you need a better oline coach used to work small miracles or just some better play.