I mostly agree with what Skeeverboy says. I think similarly to Dawn of War II, your hero should support your army, not your army supporting your hero. It's the Battle for Middle Earth, a strategy game, concentrating more on troops and large scale battles than heroes, which the LOTR games do instead. I think heroes as of right now are in a good spot and most have a specific role and some interesting or lore-accurate abilities. That said, it is not perfect, some heroes indeed are a bit lackluster, or if not the case, feel a bit lackluster, Eomer being one of them, atleast, compared to the other mass slayers. Some on the other hand feel a bit strong, but they are not uncounterable so at least that solves that problem for me.
Nonetheless, heroes in general, can still take a beating in my opinion, and 15% is noticable, but not very significant as Lord of Mordor said. A significant buff often starts from around 25% and up, speaking from my past and current modding experiences.
What I do think does add to the frailty of some heroes is the back stab and retreat mechanics. Saruman, for example, is often seen as too fragile, not only because of his role in the movies and the lore that create a too powerful for balance image of him, but also because I find him rather slow. He can take quite a few hits from most units, but if he needs to get out of there, it is not really hard to chase him down and kill him. This is what I think is often overlooked. Often, when I see Saruman, I try to bait out his abilities, inflict damage on him, then chase him with approximately two cavalry or fast units and finish the job. It seems that this is part of some of the LOTR mechanics, but if units or heroes get attacked from the back, they seem to slow down and get ''stuck'' on their pursuers in a sense and it seems more damage is inflicted on them and more fragile heroes die much faster when this happens. I think this also influences the image of heroes being more fragile.
Just blend your heroes with your armies as much as possible and keep on the micro, to make it hard for fragile heroes to get singled out is really all I can say. The ranged and melee attack argument should really be self-explanatory.
Most of you know this better than I do, but it's not so much about heroes anymore in Edain mod. Heroes are not one-man armies any longer. I am not saying it is better or worse this way, I have my own reserved opinion on that, but it is just different and it requires adjustment from the players.
Saying this, that or everything is useless or OP is just disheartening language, I think. It shows to me that you, as a player (talking in general), are viewing the gameplay experience negatively and only looking at the game for faults, not recognising the fault(s) can also be coming from your side. Improve thyself, then, when you are confident that you are on a level beyond any player at the game or mod, can you in my point of view, say this or that is OP, UP or useless.
Anyway, back on topic. I feel it is much better this way, instead of vanilla Lurtz and Gandalf slaughtering armies and heroes alike. Heroes are fun to use, and you are actually able to get them alongside your army since they don't cost a battalion worth of CP anymore.
I am far from an amazing player on BFME so, by all means, take my arguments with a grain of salt, but I feel that when I lose or make a frustrating mistake, I blame myself and strive to improve myself first, before blaming the game.
Just my two cents.