RG3 wend down with an injury because he puts himself out there more than both Kaepernick and Willson. (Vick is washed up so I'm not even going to bother to comment about him.) Too boot Shanahan basically put a desire to win it all now ahead of ensuring that the future of their organization wouldn't have to face the possibility of a career altering injury.
Running QB's are getting smarter with their thought processes with regard to putting themselves in a position to brake out of contain while not taking hits. Couple that with coaches that know how to effectively utilize the Read-Option, or that at the very least are familiarized with it. I think that your statements will ultimately prove false over the next 5 - 10 years. We shall see though.
I digress:
Personally I don't want to switch schemes if it can be avoided, but I also can acknowledge that wanting to be able to select from a larger pool of DC candidates is a reasonable conclusion to make. Mostly I just don't think it makes a whole lot of sense to retool the Defensive side of the roster at this point since we are essentially still trying to build the base roster to run the 3-4. Looking for a new DC, even in house, is something I can sink my teeth into.
Now before we all rehash again that players play, and coaches coach lets just all establish that we agree on that point; as, it ultimately is the very basic of definition for both job descriptions. Therefore we can acknowledge the contribution that players make to the season through their own personal motivations, game preparation, and playing time on the field. From that we can move on and talk specifically about Capers' job performance which I feel is the crux of the matter at hand. When talking about the possibility of him returning to the team. (Apparently his contract is up as of the end of the 2012 season, but I can't find a credible source to cite for that information.)
Capers took over after the 08 season in which our D ended the season ranked 22nd overall - missing the playoffs with a 6-10 record. In 09 there was an instant up-tick in the D and the unit finished 7th overall, we made the playoffs with an 11-5 record and were none-and-done in the Wild-card Round. The game that year saw practically no Defense from either team practically. Along with that it seemed to me at after the loss, and even leading up to it I'd say in hindsight - the players believed way too much of their own hype but they were a young D then; gotta learn lessons the hard way sometimes. Then there was the magic of the 10 season - 2nd overall D squad, 10-6 record, team record set for turnover differential, Super Bowl Champs with the crazy IR roster we had that year as a Wild-card too boot. Onward to the 11 season and we got a 19th ranked D with a 15-1 record, and are none-and-done'd again in a rather lackluster performance from the whole team this time in the Divisional Round. Which brings us to the 12 season, an 11th ranked D, a 11-5 record, and we were one-and-done this time around in the Divisional Round. This time around it was just flat embarrassing to watch at times.
If we didn't play so poorly in the playoffs three out of Capers' four with the team I'd probably be open to the idea of him coming back, however I think that resume is enough to warrant the Packers Organization to look elsewhere for a new DC. With respect to Capers' I know he has a stellar resume, however I really only care about what he's done with the Packers. Outside of 2009 and 2010 I've not been overly impressed with the unit, and the 09 loss was a huge letdown considering how poorly they played with respect to how well they were expected to show up.