There might be a little truth in what you say in the last few years. I think he is definitely beyond his prime but he is the winningest coach ever.
Yeah I remember those too - Florida State was so fun to watch in those days. They would block a punt almost every game.
Couple of notes though. The Nebraska teams of the 80's were very overrated. Their players were very strong but were pretty slow and their defense was unable to cope against passing offenses. Their option offense was also easily dismantled against talented, fast defenses. Miami and FSU met both of these criteria and had their way with both Nebraska and Oklahoma during that period.
It wasn't until the early 90s that Osborne changed up his team. I give him credit for actually becoming a lot better the older he became - he and Gene Stallings are the only coaches I know of that have done that. If Osborne had not retired when he did, I think he could have easily won 2 or 3 more championships.
When Bowden was building the FSU program, he was a far different coach than he became once FSU became a power. Around 1988 or so he became very reliant on recruiting. Since that time, when he has faced a team of equal or almost equal talent, Bowden never seems to come up on top - especially in a big game. His success against Miami is a good example.