Here are my thoughts:
1) The "it ain't broke don't fix it" argument. I am going to always use this one as long as our primary goal in this mod is mostly about improving the game, and not just remaking the game into a different experience.
So to me the burden of proof has to be on justifying the change from the base game.
2) The strategic element of the promotion. Your opinion has been that there is no strategic decision making in using the restore health promotion, where i see just the opposite.
I find early game promotions very boring. Open Terrain vs Rough Terrain....and frankly rough is usually better. Even the tier 2 promotions aren't that exciting, its really at tier 3 that things start to get interesting.
But i have found myself aching over using the health restore in early game battles.
It is absolutely true that sometimes its a non-decision. If I have no problems running, I will. If I have absolutely no chance to win, I'll heal. but there are many cases in between, and that is where the fun decision making for me comes in. Short Term benefits vs long term gain....a key component of civ.
Further i find the strategic decision gets more exciting later game with more veteran units. If i have a tier 4 unit that suddenly gets tier 5 promotions, I REALLY want those promotions. But if the unit is badly wounded and might die without healing....do a sacrifice a precious tier 4 unit to get that tier 5?
3) The "real world" reason for the instant heal. There is one real world scenario the healing can represent. We all know the classic war tale. A unit is beaten down, nearly finished off. The men rally, form up, and strike back at the enemy with a renewed vigor and defeat or severely wound their superior adversaries.
To me the insta heal represents this in many ways. Its lets a unit go from "so weak its useless" to "strong enough to do some damage or maybe even win". Its abstract, but what isn't in a civ game?