An idea that I have in my head but don’t know if it really makes sense:
The SP per mission could be distributed based on the experience of the soldiers in such a way that those with the least experience receive the most SP and those with the most experience the least to none at all, if the character is maxed out anyway.
Example, please do not take numbers too seriously, can of course turn out differently, I am only concerned with the basic idea:
Rookies receive 20 SP each
Medium advanced (level 4-6?) receive 10 SP each
Levels 7 up receive 5 SP each
Fully leveled do not receive any SP at all, maybe shift them to the ‘greenhorns’
In this way, a mixed team of rookies, medium and advanced characters will be able to adjust themselves over time.
Background:
In my current game, close to the end, I have a team (my ‘main team’) of 8 fairly mixed characters with one from the start of the game that is fully maxed out. The differences between the individual characters is quite considerable and since everyone always receives the same SP per mission little will change. The ‘stragglers’ will always lag behind the more advanced and the one maxed out character will continue to get senseless SP, which are somehow ‘wasted’ (actually he has 150 SP and i can do nothing with them and yes, he is pretty OP and can handle some missions alone).