Yes, you are right, the set ups do not require gymnastics. Just to survive long enough to be able to set it up. When you raid teams with power above 4300 time is very precious. In the range above 2500 cups if you go with 2 healers and Elradir you are not going to have enough power to take down the opposing team heroes.
Besides you just stated the problem with Elradir:
If you are not going to use him for what is one of his strengths and main purposes then why use him at all. Otherwise he could be an average (or may be better because of the mana gain on ailment) mana support hero for mono green team. And most of all like you said:
unfortunatelly aside from the mana link Elradir has no synergies with the rest of the team, which means you need a mono green team.
Generally, If the board is favorable almost anything goes. I understand the concept of mono teams but when the opposing team is quite strong even taking down the tank does not help much if you do not have constantly the right colour tiles on the board.
I do not have very fancy heroes and most of the time use a rainbow team:
4 snipers + 1 healer (fully emblemed):
Joon + Costume (Regular to have bigger miss chance)
Costumed Kiril (Costume for attack and defence down)
Lianna + Costume (Regular for most damage)
When the board is not favorable only speed, hard sniper hits (take enemy heroes before they can fire) or very very good synergy can save the battle.
Both Proteus and Gravel are great heroes. Gravel however is too weak for 5 star teams and also has to be able to fire early enough to have some use.
Proteus is more usable because becomes a distraction in a way. Against Proteus on defense you have to choose to take out enemy sniper or healer or Proteus first. So in a way if Proteus is the top priority to be attacked he gives more time the rest of the defense team to charge. Using Proteus in attack team is obviously good (if he survives long enough to fire) because Hel is a very good hero and Proteus is the 4 star one that matches the man block skill.