Rohan late game are not a match for Gondor, Dwarves and Isengard. Their swordsmen can tear through pikes with ease, add the spear throwers on to that and you have an infantry juggernaut, great if your up against a pike spam from isengard or dwarves, or tower guard spam from Gondor.
I agree that I think the Marshals of Rohan should be moved back to the assembly point, this improves its importance significantly in my eyes. Right now its not a priority to build it, and indeed its not important to build it at all.
Odysseus, I completely disagree with you about curing Théoden being a no brainer. Cruel Taxes is Rohans only economy buff, and banishing heroes is extremely useful. I often don't cure theoden until after I have unlocked the 3 hunters.