Simply put, if you can't meet Part 25 specs to fly around on one engine at any phase of flight, then you shouldn't be there.
What people are trying to point out to you is that Part 25 has nothing to do with TERP's/PAN OPS..... The aircraft is certified to specific Missed Approach Criteria, (all engine and one engine inop) as detailed in Part 25.
Prior to the AC, there was no FAA guidance telling airlines to do anything apart from clear all obstacles in the takeoff flight path. For Missed Approach procedures there was even less information.
I find it disappointing that the FAA have only issued an Advisory Circular, as they are there for information, you don't have to adhere to them. I would much prefer to see the word "MUST" used rather than "SHOULD". (Its the same with AC-91-6A regarding contaminated runways!)
Airbus757, even before the AC, we were reducing landing weights to comply with Missed Approach Climb Gradients in certain airports, even though this had a significant commercial impact on the operation.