you currently don't get XP for hitting neutrals or friendlies
And I find that to be unrealistic hehe. There's no logical reason why shooting friendlies or neutral units shouldn't award exp, and you already get punished with negative score if you do that.
I seen that being done to a single enemy 20 times in one round on one stream
That looks like an exploit, right? But is it really?
1. Only the small minority of players use the revive+stun training tactic, because it's a huge waste of their personal time. I've also seen JS+SM streams where players were whipping downed enemies, but other than that, practically no one was reviving enemies for exp. If this was a highly-beneficial exploit, then a lot of people would be using it.
2. It's costly. It's not free, because you consume freshness every turn, lose glamour, and there's a chance of the stunned enemies dying. It's also not 100% safe, beause there are still live enemies on the map, while your units lose morale. You may end up with your panicking units running somewhere and getting shot, or the stunned enemies waking up and you not having anyone nearby to stun them again. I've seen players fooling around and getting burned this way.
3. The few perfectionistic players that use the training tactic do have a lot of fun doing that. You'd be taking away their fun, and prevent them from achieving... what? Reaching stat caps faster? If reaching stat caps fast is a problem, there are other ways to mod that.
4. It's inconsequential. As I mentioned before, the majority (>95%) of the game is played after units reach the stat caps. Your perception may be skewed if you only look at streams of people playing the early game.
5. It's not immersion-breaking. What is immersion and how does it get broken? In this context, we're talking about the consistency of game mechanics. A player will have their immersion broken if a game mechanic is bugged, inconsistent, or otherwise unpredicatable to the player. The player will have their game engagement disrupted if they find a game mechanic to feel unrealistic, unnatural or forced.
Shoot at a target to get exp
Shoot at a unit to get exp
Shoot at a unit and hit it to get exp
Shoot at an enemy unit and hit it to get exp
Shoot at a standing enemy unit and hit it to get exp
Shoot at a standing enemy unit that hasn't yet been unconscious and hit it to get exp
The more conditions you add, the less realistic a particular game mechanic becomes. Does that make sense?
Of course, a game doesn't need to be immersive to be fun to play. People who play on JS+SM play it for the challenge, and the type of fun you get from beating a hard challenge is completely different than the one you get from experiencing a deep story.
Would making this change (preventing revive+stun training) make the mod more fun to play? For me personally, it would make it a lot less fun. At the same time, I don't see what sort of game balancing benefits are there. It wouldn't make any missions easier or harder. Especially in the early game, it feels like a good tradeoff to sacrifice freshness and glamour for extra soldier exp. Does this tradeoff break the game balance in some way?