My disagreement is partial. I'll reference the following link to 2010 highlights (when both players were at their best) in my comments:
You must be logged in to see this image or video!
To your point, the play at 2:10 in that clip is a representation of Hawk doing the job you attribute to him. Unfortunately, it's hard to find the low light clips. Too frequently, Hawk does not get off the blocker as well as we see in that play. As a consequence, when you see Hawk at the second level it's too frequently chasing from behind or late. He scores a lot of irrelevant assists. Hawk does not so much "clean out those pesky blockers" as hang back to be engaged. He's more the guy who makes tackles from behind on 15 yard gains rather than stopping them from happening in the first place. I would characterize his play when Bishop is present as "working supervisor". He was asked to do more in Bishop's absence, with mixed results.
As far as long speed is concerned, Bishop's better than the 4.8 you cite. He pulled a muscle at the Combine which is why he did not run the 40 there. I suspect he was not fully recovered two weeks later at his Pro Day. To illustrate, see the Bishop pick at about 1:06 in the above clip. Note the additional gear he kicks in at the 20 yard line when he senses a tackler closing on him. That ain't a 4.8 guy. Compare the speed evident in that Bishop pick to the Hawk pick at 0:40 in that clip...there's no Hawk juice, no next gear, turning the corner. By 2010, Hawk could not recapture that Combine number. He's even a bit slower now than in 2010. It's generally recognized Hawk has lost a meaningful amount of the speed that made him a high pick. Are you certain YOU watch the games?
I think Hawk draws a bit more abuse (just a bit) than he deserves because he did not play up to the post-2010 contract. He's OK at best in the run and cover games though his ball skills leave something to be desired, and he is not an effective blitzer. He doesn't make plays...of his 8 career picks in 7 seasons, most have been gifts (see clip for examples). 2 forced fumbles in 7 seasons. 13.5 sacks in 7 seasons. I don't think there is player in the league who has taken as many snaps as Hawk and has made as few impact plays.
Bishop is not without blemishes, but when you watch the above clip it is clear he's the more dynamic player. In the run-blitz-cover equation, he's the best we've had inside in a long time in the first two aspects of the position. I've already acknowledged he's not that great in coverage. I think it's a case of how one's greatest strengths can be a weakness...Bishop can be characterized as a straight line burst player, which is certainly a virtue closing on RBs and QBs. Being that kind of player often does not translate to staying with a receiver out of his break. He's not Pat Willis, but close enough to be very valuable.
In conclusion, I believe the general perception that Hawk is not carrying anybody's water is correct. Water carriers do not take pay cuts. His comments after the fact seemed to indicate he thought he deserved the cut or was fearful of not even being around for 2013 if he didn't.
Again, I think "working supervisor" is an apt characterization of Hawk's play.