Centaurus, you are right in principle, a seized prop isn't as good as a feathered one. but how exactly is one supposed to diagnose a 'major mechanical fault' before commencing any immediate action drills, particularly after takeoff?
Why risk botching it up and feathering the wrong engine?
The drills all the way through to feather shouldn't take more than 5 seconds for a well-practiced pilot. And getting the gear and flaps up is just as important as feathering the prop.
Why delay all these items to take the time to consider whether the prop will seize first? You simply can't train someone to knee jerk react with proper checks and drills as well as have them consider the possibility of having to feather immediately if the revs are dropping below min feather speed (somewhere around 700rpm or so I seem to recall from most I have seen). They are conflicting commands. You can either stop and think about it. Or do the checks. I'd rather fly the plane and do the checks immediately. If the prop stops that quick, there probably wasn't much I could do about it anyway.
As for in the cruise, well is a seized prop in fine pitch really that critical? You're going to have to come down anyway!