I mainly start any total war game on m/m. If i do it on anything less i find that the ai just invades on the spot without any diplomacy.
Thinking about FPOE's starting position and eventualy when i get them to become arnor and i have eliminated the two orc factions next to me apart from isengard i find it hard to think that i will get a chance to really use arnors army to its potential unless the other evil factions have managed to work their way towards me. I can just imagine that i get arnor to reamerge and i get wedged between three to four good factions without any big good vs evil climactic battle, but that could just be me