Hm, I disagree with a lot of this. Seems like we're going off of tackles, stats, etc, and not paying attention to the way players play when they're not the ones in the spotlight. Zimmer's style is hard to evaluate, because more often than not, your job is not to get the tackle/sack, but to set the edge and force a comeback, or stay home in the zone to prevent a scramble. I'll go down the list and explain further.
*disclaimer - I've said this before but it's not a popular opinion so it bears repeating. I go more by what I see on the field (or what I can make out on TV) and less by stats, PFF grades, etc. I also frequently watch players away from the ball, or track a single player from whistle to whistle to evaluate them.
You say he's had a disappointing year, and I'm not quite sure where that's coming from. He's provided a rush that gets double teamed unbelievably often, which frees up the Ends to get one on one matchups. Griffen's had a great season largely due to this- give a guy enough one on ones and he'll win his share of them. If anyone's been disappointing on the line, it's Robison, but it makes a little more sense since he's getting older. Joseph doesn't often gets sacks, but he does draw inside double teams, which is exactly what we want out of him. When Zimmer talks about "team players that do their job instead of going for the big play", this is what he's talking about. Floyd is a monster in this regard too. Sacks are a unit stat, imo, and more often than not, Joseph is an assist guy, not the shooter.
I'll admit I've probably been too hard on him, but what can I say? He's constantly out of position. Whenever he blitzes, he misses gaps and gets caught up in engagements, taking himself out of plays. He's below average in coverage, and gets burned a lot (though man-to-man is always tough for linebackers, to be fair). He's also often greedy, leaving the middle of the field wide open for a checkdown or scramble. On the run, he's terrible at taking angles and overruns a large number of plays. Not a lot of people talk about him amidst Hodges, Greenway, Cole last week, Barr at the beginning- but that's because he's not in the plays he's supposed to be in. Our rush defense suffered greatly because of this, and it's also a big reason we got shredded up the middle a number of games. He should live on special teams, if you ask me.
Blanton came along... okay. He was downright awful at the beginning of the year. Safeties that lead the team in tackles are liabilities. A large number of those tackles came after he was a step late to picking up routes, and he'd get the tackle after 15+ yard gains. Sendejo is even worse at this, and I'm not a huge fan of his athleticism (as jacked as his arms are). Again, we're paying attention to the few plays they make because it's the only ones we saw, but it's when the players aren't where they should be that coaches notice. When Zim says "we made tons of mistakes, out of position, etc" he's talking about this kind of stuff.
I don't feel as hopeful about getting him back. Asking a perennial starter to take a massive pay cut to be a backup is a tall order. If we do, I'd be fine, but he'd be in competition for sure, and I just don't see any veteran of his status being willing to take that over
This is another misleading one. He got burned a lot, some were real bad, but he also had some games where it seemed like they never threw to him, which is exactly what corners should do. I won't try to defend him too much though Cap is definitely a question mark. It isn't unwise to give him another year to gel with Zim and co. If Zim can turn Josh Robinson around, he can figure out Captain. On the other hand, we have money to go snag another big, tall corner. If that's easier than trying to develop a struggling pipsqueak, we'll do that.
D Line depth is something we've been good at since I can remember. We definitely have great depth LBs at least with Hodges and Cole, though I think they both get to compete for starting jobs and have a reasonable shot at it. I still want to go pick up an MLB, since we could really use an anchor at that spot (especially if Greenway doesn't stick around).
Where other good linebackers were picked isn't really important. It's also pretty hard to say what we're going to pick before free agency. We could be looking at all these linebackers and wideouts, and then go get Maualuga and Dez and shake the whole thing up. Depending on FA, we might just trade back or go best player available. Trading with a playoff team for another 2nd or 3rd seems real sexy to me, since a lot of our needs can be filled in the later rounds (for example, a Safety can take time to develop since Harry and Rhodes can bolster the secondary and make up for rookie struggles, to a point).
When Zimmer talks about defense, he talks about teamwork, being unselfish, playing as a unit, etc. This is why it's important to look at players who weren't necessarily making the plays, but enabling them.
So if you ask me, here's what we do.
D-Line: Don't touch it too much. They've got a talented unit, although they had some games (most of the divisional ones, actually) where they got bowled at the line. ToP had a lot to do with that though, and they're mostly young except Robison. Maybe draft someone in the middle rounds, a project that can develop behind Robison for the next few years just like Griffen did.
Linebackers: I'll assume we don't keep Greenway, because I'm a Vikings fan and I'm afraid of optimism. That leaves us with notable players: Hodges, Barr, Cole, Brinkley, Brandon Watts. Brinkley should be cut, and I'm pretty adamant about that. I like a competition between Hodges and Cole on the outside, and I really want to get Maualuga. But if that doesn't happen, Hodges-Cole-Barr with a 2nd or 3rd round pick in there to compete seems serviceable.