From Singletary's last year (2010) to this year, Harbaugh has replaced three offensive linemen while turning the other two into pro-bowlers. He's replaced four of his front seven on defense (moving one of the keepers from NT to DE), and he's replaced three of his four starting DBs. That's a change 8 of 11 defensive positions. On offense, he kept Gore, and managed to turn Smith and Crabtree into productive NFL starters. Now he has his QB under center and the offense looks like the NFL's best. At this point on offense, he's changed the starters at 6 of 11 positions.
Harbaugh walked into a situation with great lines, a good running game, and a couple of fine defensive players.
He had a mediocre to average QB in Smith and average WRs in turns of NFL production.
He took a chance on Colin. He wanted a Cam clone and he worked out for him.
Rivera walked into a team, inspite what a lot of people like to think here, that just does not have that type of talent on the lines.
Great lines do wonderful things for football teams.
This free agency period and draft will tell us a great deal about Rivera and Gettleman. Do I see Rivera ever being in the NFC Championship game, sadly no. I hope I'm wrong.
Do I think Cam can ever have the type of evening Colin had, I don't know, I hope so.
In short, in his two years there Harbaugh has pretty much overhauled the entire team and raised the level of play across the board. And he's done it while winning and winning big both years.
What's Rivera done again? If I recall correctly, he cut Otah, replaced Martin with Nakamura, and signed a bunch of ex-Chargers.
But again, the reason Harbaugh has done well is because he walked into a situation where he had a ready-made team, and I'm sure everyone here believes that if Rivera had gone to SF instead of Carolina, he would have had the same results.
Do I understand your position correctly? Just want to be sure...