I'm not a parent and have no idea what is practical or possible, nor do I have any particular interest in the detailed mechanics of diaper changing. I only know that public diaper changes outside of airline lavs are disgusting, unsanitary and potentially dangerous.

Many experienced parents in this thread have described alternative means for diaper changing that don't involve doing it on seats (whether passenger seats or FA jump seats, i.e. the "padded bench" of the OP). These parents are also, obviously, experienced fliers, like most of us on FT. From these two facts, I conclude that any contention that the only way to change a diaper is in a way that constitutes a nuisance to other passengers and crew and is incorrect.