Sorry, but I think you are too easy on Holmoe. According to him we were a couple or more very good recruiting classes away from having the defense where it needed to be, and yet, the next year it was good. (because he hired a DC who told him to shut up, get out of the way, and give him every player on the roster he wanted.) No one expected miracles out of Holmoe's defense. But there is a middle ground between miracle and 110. He was awful. And then when he decided to take over special teams, it immediately became the worst unit on the team.
Holmoe would never have developed into a good coach. Maybe he could have after years of intense study learned something about X's and O's. (maybe) But bottom line he was weak. Weak character, weak everything. He seemed to have a huge inferiority complex and was constantly giving us reasons why things can't be done and why Cal was a place that sucked to recruit to because, well, basically Cal sucked. He never took responsibility for anything.
I dispute that Holmoe was a good man. Nice man, maybe. Well intentioned, maybe. But good men don't let their players get abused by their assistant coaches like that. When I read later Holmoe being quoted as saying that he knew after his 2nd to last season that he wasn't going to be able to make it work, I was done with him in terms of the whole upstanding thing. Apparently Kasser wouldn't let him quit, the last in a long line of people, many of whom he had the ability to fire, who wouldn't let him do things.
Basically he stood in front of alumni and parents of players and said "I'm a nice man and I care about my players and I will teach them to be upstanding citizens" and some people bought it. Then he sat and watched their football careers wasted and meanwhile did nothing to help his players to get through academically and had a horrible grad rate.
You are right that Gilby tanked the program and Holmoe did not. (well, sorta, Gilby took us from top ten to bad, but Holmoe took us from bad to atrocious - how many Cal coaches have lost 10 games in a season?) That was merely because Holmoe did not have the opportunity. If Holmoe took over for Snyder it would have been tanked far faster and I don't see any way Holmoe takes a team to 9-3 like Gilby did, even if the roster was handed to him.
As for the rosters both guys left, well, Gilby left Cal with Tony Gonzalez, Pat Barnes, Bobby Shaw, Dameane Douglas, Ryan Longwell, Matt Beck, Tarik Glenn, Brandon Whiting, Jeremy Newberry, John Welbourn. All of those guys except Beck had at least a couple years in the league, some long careers. So it wasn't completely bare (though there were certainly issues). Holmoe left some good players too (though some of them he didn't realize were good or didn't know where to play them.) But there were large holes as well. Remember Tedford filling up the two deeps with JC guys? Rodgers, Makonnen, Arrington, Giordano, Riddle, Maningo, Blay-Miezeh, Cross? By 2004, which should have been filled with Holmoe's upperclassmen, 12 of 22 starters were Tedford recruits. Holmoe had recruiting classes where you'd look later and see like 4 guys still on the team. They'd be a good 4, but there'd be nothing else left.