EDIT: Having doubled my time playing the mod I can now say that it is indeed supposed to remove the EXP reduction whenever you get a non-summon hit on the creature. That being said, the experience I described below was a legitimate one. I'm guessing it was some kind of bug but I'm not sure. Regardless, I leave my original post below in it's entirety so that it can potentially be used to find the bug and also because I stand by the core sentiments of the post. I do not believe the reduction is a fair one, because while it's fine how it works for the early stages of the game (when it's working as intended), the end-game levels will be all but impossible to grind as summoner when your summons will more often than not be getting the kills before you can tag the enemies. And I do still believe the attitude of those responding to these concerns to be lacking.
I'm really not a fan of the way minion kills give reduced EXP, at least not with the way it is currently handled. I understand that it's a preventative measure to keep people from afk farming EXP using minions but it drastically puts summoner at a disadvantage when it comes to gaining EXP during active play. I've seen in multiple posts that hitting the enemy at least once before the minions kill it will remove the modifier and give you the normal EXP amount for the kill but in practice it seems this does not work with just a single hit, it seems you need to deal a certain amount of damage or a certain percentage of the enemy's max hp before you will get the full EXP reward. As things stand about half the kills I get during active play give me normal EXP and that's only while playing extremely risky; Add to that the fact that this will only get worse as you progress into the later stages of the game and eventually I'll basically be getting all my EXP at a reduction of 90%. Because of this, summoners have to do about 5~10 times the amount of grinding just to get to the same levels as any other class, and that's on top of the fact that summoners are already the weakest class available in the base game due to poor implementation. The only way to avoid this problem is, ironically, to afk farm EXP. If I'm already going to have to pour 5~10 hours of grinding into the game just to get the same amount of progress as another class gets in an hour, I may as well make it a guaranteed 10 hours of grinding and do it while I'm afk.. But the whole point of this is allegedly to prevent afk farming, so why stick so much to a system that in the end only incentivizes it?
I say 'allegedly' because I don't think that was really the intent. In nearly every response to someone bringing up concerns with this mechanic (both here and the standalone version's thread) there is no discussion being had, the person responding only says something along the lines of "It's intentional" before moving on even when the concerns being brought up are as nuanced as the complaint I made above. People (at least, most people) are not arguing that afk farming for EXP should be allowed or that the reduction should be removed entirely, people are arguing for a better system to prevent afk farming that doesn't heavily nerf the summoner overall. It's already a pain to get enjoyment out of my favorite class in the base game, and this "intentional mechanic" is only making it harder to get enjoyment from the summoner at best and making the class totally unplayable at worst. And it's very hard to see it as nothing more than a method to dissuade people from afk farming when no one is seemingly willing to have a discussion on the matter. (And no, I don't consider cold dismissal to be a form of discussion.)
If the mechanic is not going to be reworked or replaced, at the very least it would be nice to have some way to configure the reduction. I don't think it should be 10% by default, but even if it is 10% by default.. being able to adjust it to at least 50/50 in the config would be a godsend. It doesn't fix the fundamental problem with the mechanic but it would certainly make it a whole lot more bearable.