If your going medics....you go medic, meaning you always pick up medic 2 as soon as you can. And part of the run back to friendly territory....sometimes that's not possible, sometimes you need that mainline unit to hold out for one more turn, and getting +15 HP instead of +5 is often literally the difference between living and dying. Happens all the time.
Or sometimes your melee unit in the front takes some damage, but is fortified. with a medic 2 behind them they recover 15 hp vs 5, triple the difference, and yes that really starts to matter when you have a siege and those frontline units have to sit there taking the pain.
My calculation was specifically based the basis of "retreat and heal" which was the the premise of the statement of medics doubling or trippling the speed those units get back into the fight.
A fortified unit is a different scenario where they stay in position. Looking specifically at having medic on a melee unit where we look at generally as values change with unit strength and also depending on the unit they are defending against and the territory they are in but the malice for a melee unit having medic usually outweighs the additional healing especially if they are under serious attack and usually means they are more likely to need to withdraw to heal sooner so it is not an advantage but actually a net malice promotion as currently stands and actually becomes a worse promotion over time as the negative effect scales with unit strength and also additional ways of adding extra healing are added as the game progresses. Promotions wise additional combat score (apart from select scenarios which tends to involve more micro) outweighs having medic on a unit.
There is no issue about choosing medic on none front line units apart from that seems the only choice with the current medic promotion, which is the problem i have specifically where having medic available on melee units is a false choice or as someone else already put it, a noob trap.
Personally i find that by the time i have the opportunity to get medic 2 on archers it is a poor choice as it is delaying much more game changing promotions even more as the best defense for your melee units is being able to hit and kill enemy units with more of your ranged units, my scount or scouts have come home with medic 2 so they can be used instead and at that point and the unit cap is high enough that i have adequate supply to effectively cycle units through the front line and allow them to heal and a well built road system to facilitate them doing so.
In short i see medic promotions as not competing well with other choices as it stands and as part of the fun is making decision, when there is in effect no decision it is less fun. Before the mailce was added i would scatter medic promotions around my units (including melee), now i never put them on melee units and only ever go to medic 1 on ranged units.
I like
@nekokon idea of allowing medic to lead to higher tier promotions like range for ranged units so it can be a core unit which heals or a core unit which does more damage rather than a subpar unit which heals. Considering it usually requires basic tree branch level 1 to take medic why not allow it to take the place of basic promtion tree level 2 and 3 and then move onto to the advanced level of the tree so you still take the same number of promotions to get to the more game changing parts but you have a choice of how ypu get there?