Why?
If the point of the ability is to mechanically support a certain character achetype for the player of the fighter, why is it necessarily the case that I want NPC warriors to have the same thing?
I think it's worth noting that "How can I learn that spell the bad guy wizard cast at me? -Oh, I can't??" was a HUGE complaint in some 4e games. "How can I learn that sword maneuver?" didn't come up as much, but I can easily see how many players (and some dms) find cleaving npcs' abilities from pcs'
just based on the fact that they are, or are not, pcs highly irritating and hard to fit in the in-game fiction.
Huh? It's always going to be the case that some PCs can do things that some monsters cannot (eg no giant rat can cast meteor swarm). And vice versa (eg there's no way in Basic D&D for a fighter to get +2 to hit from a berserker rage).
Right, and that's not what anyone is arguing. The argument is about much more similar cases: that down-to-3-hp-last-stand-guarding-the-bridge scenario mentioned above
just doesn't work if the npc bad guys are using the same great weapon fighter rules that the pcs use, especially when the npcs are the trained warriors of some mercenary force who, by all means, ought to be treated as... fighters.
Now, that scenario being off the table- is that a terrible thing? Not always, and not for everyone; but clearly it bugs some people, and equally clearly it speaks against taking a heroic last stand in such a (perfectly cinematic and genre-appropriate!) manner.
I'm not wed to either side of the argument here, but I do think it's worth paying attention to both the fact that some gamers find the pc/npc dichotomy jarring/annoying/immersion-breaking (especially post-3e) and the fact that DoaM
does affect what playstyles the game supports.