Tyres,
There are a whole raft of reasons why you wouldn't necessarily descend to FL250 after a pack failure enroute.
The MEL restriction is a "boots and braces" method of ensuring that the aircraft is operated conservatively with a pack U/S it does not require the descent of the aeroplane if a pack fails in flight
Descent would, or should, certainly be part of the decision making considerations, but a decision not to descend should not be universally condemned as "bad airmanship"
The "airmanship" chestnut is interesting because what I consider to be good airmanship is entirely different to the next bloke - and so on..