I agree that OL is the biggest concern, though I'd argue it's a coaching concern anyway you slice it. I think people (no this post specifically) quickly point at talent. Is it true in this case? maybe, but even so, we're now far enough in where we either need to have landed the young talent and be seeing the results or we should have loaded up on JUCO kids to help as a stop gap. It is such a huge part of an offense that you can't, IMO, be saying 'we just don't have the talent here' 4 years in. A little light on talent? Fine. But having not enough talent to put together a pretty average group? Not fine.
My runner up concern remains pass rush. Surprised it hasn't been mentioned so far.
Other thoughts:
I like the secondary but just think secondaries tend to be fairly dependent on pass rush. No one gets excited to see DBs make tackles 7-12 yards downfield all game. Regardless, I really like Lyn as a CB and while I'm not entirely sold on Anderson, I think he can be a fungible part of the secondary. Thomas is a nice player and, in Reddish, Desir, Eskridge, and George you have four pretty intriguing young prospects. Jury's out a bit on Mugwa and I'm not real high on Wilkes, but I think this group is at least intriguing. I'd be surprised if we aren't talking about them at mid-season as at least being talented and improving.
Special Teams and depth. I get why people make the connection here but I'm not sure I buy into it. I mean, how often are special teams the way that less talented teams upset the big boys? Happens all the time. I tend to think it's focus and execution first and I'm not sure Marrone was quite as focused on Specials coming over from the league (perhaps rightfully so) and we're still playing catch-up. I could be wrong, but things like gaping holes in field goal protection for multiple games don't scream talent deficiency to me. And if KOs are such a problem, as they have been for almost DM's entire tenure, at some point you've got to find a way to fix it. This is not an anti-DM rant as much as an argument that talent may be a factor but there are other issues here.
Youth/inexperience won't be an issue at RB. There may be issues in our backfield. I'm not entirely sold on Smith, though I love Gulley (which probably seems strange). Regardless, young kids can play at this position (as well as in the secondary and at WR, etc.). The question will come down to talent and line play. I think we'll have decent talent at this spot.