I think that you missed the point of the exercise, which wasn't about evolution per se, but about irreducible complexity, a feature that ID proponents say shouldn't be present in biological systems if they arose by purely naturalistic processes.Miller's mousetrap argument is nonsense. Irreducible complexity says nothing about starting from a more complex functional system and arriving at a less complex functional system, which is what Miller is illustrating.
Behe was trying to illustrate what irreducible complexity was with a mousetrap. Even had he been successful, all that he would have accomplished is to illustrate the quality that he was claiming is found in biological systems, not that it actually occurred in living things.
But Miller showed Behe how unsound the claim that something is irreducibly complex is absent any rigorous, algorithmic, deterministic method for determining when that quality was present . At present, all we have is people declaring that some systems are irreducibly complex because they haven't identified functionality for any combination of parts less than the entirety, which is not the same as saying that none exists.
It was perfectly appropriate for Miller to begin removing parts - reducing the complexity, if you well - to demonstrate that irreducible complexity was not present. The claim was that if you remove any part of a mousetrap, it is no longer able to catch mice.
Miller demonstrated not only that the absence of reducible complexity might be difficult to demonstrate, but that even if a simpler mechanism couldn't catch mice, it didn't make the device irreducibly complex if subunits had other functionality..
The fact that Miller was able to reduce Behe's five piece mousetrap to smaller and smaller mousetraps was just theater. All that was necessary was to show any useful function for the less complex mechanisms, such as serving as a tie clip.
The challenge to ID proponents claiming that some complex system is irreducibly complex will always be to demonstrate that that is the case, something that may be impossible to do even were it true.