So this looks interesting! Some good points have been brought up about exceptions, though - carriers, the player ship, and so on. (Say, SO ships kitted out for escort duty?) I still think this might work, actually, with tweaks for all the special cases - or perhaps some elements of it might be useful. The thing is, peak time degradation - and when it happens - is hidden enough as a mechanic that I don't want to make it more complicated.
In the next release, some things should combine to - hopefully - make this less of an issue. Smaller (but more elite) enemy fleets on the high end, and some skills that also factor in. For example, there's a piloted-ship skill that gives (in addition to other bonuses) a flat bonus to peak time, which benefits small ships more. And there's another skill that boosts the peak time of some frigates specifically. So, all in all - I think this is an interesting idea, and I'll keep it mind. But, I think it makes sense to see exactly how things shape up in the next release.