You weren't discussing Briggs and Tillman at the end of their careers. Your statement was that in their primes Briggs and Tillman were still on mediocre teams. The clear intent was to somehow blame them for that mediocrity. So I picked a player who played much of his entire career on mediocre teams to point out the stupidity of the argument. The fact the team was mediocre according to you during their primes had nothing to do with Briggs or Tillman and you know that. So it's a stupid argument.
Good teams play the best players period. The Steelers brought 36 year old James Harrison out of retirement to play for them and they made the playoffs. The year before that he was on the Bengals who also made the playoffs. No one is suggesting the team field a D full of 35 year olds but the idea that goods teams never play aging players is frankly a stupid one.
So again, your logic is flawed. The issue is not Lance Briggs' age. The issue is whether he is still good or not. Also Vince Wilfork played 765 snaps and Justin Smith 715. They were both top 15 in snaps for 3-4 DEs. I would hardly call that part time.
I never blamed primetime Briggs and Tillman for the mediocrity of those Bears teams.
This can't be a hard concept to grasp. Successful teams don't field old players on positions that rely on speed and quickness.
Re: the Steelers - they did that because of injury (largely to a fast ROOKIE - a young guy). It means that there were no other younger better players on the street. Not to mention that Harrison played on that team - under the same HC and same DC - for 9 seasons. Translation: he knows the defense. He was also in football shape. How exactly does that compare with Briggs? Was Harrison injured for two straight seasons prior to this? Did Briggs play for the current coaching staff for 9 years? A more apt comparison would be if Lovie/Marinelli signed Briggs to Tampa. Harrison won't be on the Steelers next season. You are comparing apples to oranges.
The issue IS Brigg's age. And his injuries. And his lack of conditioning. And his lack of speed. And his attitude. There's a reason you don't see 35 year old starting LBs in football. Especially ones that just came off of two season ending injuries and ones that can't be bothered to properly condition their 35 year old injured bodies.
As for Wilfork and Smith - they are DTs, not DEs. DTs play part time by trade. They are not linebackers who rely on speed and quickness.