A78, there is no “your world” vs crab’s military world (at least not this time round).
I admire your patience. You are of course 100% right. And crab didn’t read the book.
The MTOW (of 2500 lb) is not a power limit. The power margin is not the difference between the actual weight and MTOW, but between the actual weight and the weight the engine could lift under the current circumstances (disregarding MTOW restrictions). Or as you correctly pointed out, by the difference between the current PA and the OGE ceiling at the current circumstances (which was massive).
The only limit was the pilot’s lack of skill and recency.