The defense, as it stands, is doing a pretty good job. The new LB's, as they stand and with all their faults, are doing well enough as a part of the defense that we have been excellent against the pass and excellent in points against (the most important defensive stat). Our defense is a solid unit and both of those much maligned LB's are the guys playing the most snaps.
Have they been great individually? Of course not, especially Wheeler - when he makes a mistake, it is amplified. Are we significantly worse against the run? Yeah, definitely, and the two new LB's are a major part why. But we're also much better at getting stops and we are much better against the pass... and we are better at points given up. Both guys have been consistent enough that they have been on the field more than anyone on our defense, a defense that is ranked 8th in points allowed.
Even if we changed nothing to the defense (meaning we hypothetically kept all the same players), I would expect the team to be improved next season with better/more depth at CB and more familiarity with our system/players for both Wheeler/Ellerbe. I expect Wheeler and Ellerbe to get better next season.
Our biggest concerns are on offense... we need a whole new OL, at least 1 new RB, a FB, and maybe 1 more TE. Considering we are going to need 3-5 starters for just the offensive end, that's a lot to address in and of itself. Our offense is ranked in the bottom 15 in almost every single meaningful statistic. We can't sustain drives, we cant run the ball, we cant protect the quarterback, and most importantly of all, we struggle to score points. We have a lot to address on the offensive side of things.