> 7. Healing/leadership should give experience
> It is felt that allowing units to gain experience without risk would make leveling-up of such units inevitable. Further, one of the motivating examples of this is so that units such as shaman can have a hope to level up in multiplayer. It is pointed out that if the experience gains were high enough to allow shaman to level up in a single multiplayer game, then it would be trivial to gain the best type of healing unit in a campaign very quickly.
https://forums.wesnoth.org/viewtopic.php?f=12&t=34904#w0fpi7 (2011)
> I know you can kinda cheese it by reducing a monster to 1-2 HP
In practice, I've found it difficult to get monsters to 1-2 HP since it often means not using your most powerful attacks. On harder difficulties I usually can't afford the opportunity cost.
Edit: Now that I think about it, most turn-based games have this mechanic. It's almost an idiomatic balance/design decision in gaming.
Compare to Dota where support heroes have acquired more and more opportunities for assist gold/XP, it does in some sense make the game "easier" for the support players, but then the game is harder in other ways because now the supports are all way more farmed and dangerous than in older versions. It's the difference between controlling an army of many units and having to manage them all, versus controlling one unit and needing to work together within a team.
> I know you can kinda cheese it by reducing a monster to 1-2 HP and then getting them to attack, but it feels like going against their role.
This is a problem with the XP-per-kill system. Wesnoth could use a variant instead. I use the above strategy all the time to level the healers up.
Note that elven units have slow (their healers), which is very powerful in its own right for getting a kill on a unit. First slow, then deal damage with other units.