I would like a way to salvage mercenaries you can't complete for coins

There are some heroic´s I just can’t complete. I would like an option to salvage these mercs to get coins for the others.
You have made some very difficult bosses, and I am tired of even try anymore. So might be a idea to salvage those I can’t complete to benefit others with coins. Or just make an option to delete them, since I hate have something I can’t complete in games.

I can list the bosses here, but you never seems to nerf those that is insanely hard.
Here is the list of those i have no chance against. Most of them I cant even get to the bosses: Heroic versions.
Onyxia, Captain shivers, Dragonbone, Silas Darkmoon, Sayge seer of darkmoon, Ichman, Fish of N´zoth, Garrosh Hellscream, Yogg saron, Darkmoon rabbit. The curator.

Most of these are the climb to them I can´t do. But a few of the bosses also wipe my team, some of these require you to hit the best treasures which is hard to get when you do these with mercs in the party you carry for weapons. Often the treasure i get is to the mercs I do not use in the party.

I like mercenary mode I just hate I can not unlock some weapons, so would rather get rid of those mercs than have them to look at. The mode was 10 times more fun before you made the weapon unlock changes. Back then I played it a lot of hours each day. Now it’s just a game to see how many different ways you can wipe your team doing weapon unlocks until you give up.

I would like some nerf to this or a way to remove the mercs i can not complete, and make other ways to unlock these weapons. I would rather buy them then spend a second more trying.