Let's see what we have. Two journeymen QBs, neither have stuck, after each being given huge chances by their last two stops. A rookie QB that is at least a year, probably two years away. An offensive line that has taken a huge step back after losing its best lineman, best depth lineman and replaced them with UFAs. A TE corp that is way below mediocre and its best player is coming off major surgery and may not be full speed till half way through the season. One established WR (a #2 on most teams), a second year guy with bad hands, and three rookies. A backfield with two gifted RBs and no FB. Throw in a O Coordinator with zero pro experience and is younger than some rookies, add in a completely new offense that requires experienced lineman.
If you think Kolb, TJax or Manuel is the answer you are answering the wrong question. The question is outside of RB is there one area of depth or experience in this offense. That answer is no. This offense will be a cluster F till midway through the season after which it may achieve mediocrity.