Why should the offense call a timeout in the middle of series when they have game planned and should know the playbook.

Defenses get gassed, you can't do more cardio during a game.

Offensives mix up play calls, you can't go back and study the playbook during the game.

I don't think there is anything inherently wrong with a defensive or offensive TO. You just hope you don't need to use either, so that you have them for the end of the game or half. There are inevitably critical junctions in a game where, while on defense, you may NEED to use a TO. A goal line stand (re: BSU; possible the greatest goal line stand in BYU history), a 4th and short, etc.

In Bronco's case, since he was so D oriented and calling the plays, he probably got too involved with the D and would call a timeout at questionable times.

Either way though, I honestly don't think it matters. Calling a TO outside of the final 2 minutes in a half or the game is a risk, whether it is offensive or defensive.