Two things:
1. I've lived next to mountains for over 20 years, and you're all right. Here at the Rockies there are a great deal of steep, rocky crags that are difficult for a man to scale, let alone a horse. That's why we've found and used mountain passes - they're easier for horses/wagons/cars to travel through. Believe me, battle on any of the mountains around here would suck - especially on horseback. They are extremely steep in many places. Running through them with armor on would quickly wear you out. We have an exercise trail about 15 miles from my house they call "the incline," which travels vertically up the side of a foothill. It's one of the most arduous and difficult trails in the area. Again, would hate to have to fight up one of those.
I've also been to "mountains" in the UK - most of which (the ones I visited, anyway) are decidedly
not steep or rocky. To me, after living around and hiking "fourteeners" (peaks at or above 14,000 ft elevation), they were no more than gentle, sloping hills. I've been told (never visited) that the Appalachian Mountains in the eastern US are also more gentle than the Rockies.
So it really depends on the location and age of the mountains in question.
Examples of rocky crags (foothills, not even in the mountains yet):
(Crags in the background)
And links to mountains I live around (Kingston Peak and mountains in Roosevelt National Park, northwest of Denver, CO - and the people in the pics aren't me or anyone I know):
http://home.earthlink.net/~pushkin/pages/Imgp0390.htm
http://home.earthlink.net/~pushkin/pages/Imgp0394.htm
http://home.earthlink.net/~pushkin/pages/Imgp0395.htm
http://image08.webshots.com/8/8/52/51/2499852510021435239fJMgTy_fs.jpg
http://image53.webshots.com/453/8/13/58/2829813580021435239dcAtOY_fs.jpg
http://image09.webshots.com/9/3/25/36/2362325360021435239CPhZDi_fs.jpg
Because I've lived around the Rockies for most of my life, I can relate to and enjoy the mountains on M&B. I'd rather keep them - but I guess what really matters is the age, composition, and origin of the mountains in question . . . or Armagan's preference/experience.
2. So historical armies/warbands wouldn't want to fight in mountains. So many people on M&B don't want to fight on mountains. So don't fight on mountains. Makes sense to me.
NOTE: Don't get me wrong, an incline in the direction of the peak and a broader view in the direction of the plains would be a great
addition (not sure of the feasibility in the battle area, but would be cool) -
but rocky, pointy, "cliffs-on-both-sides" terrain is not unrealistic.