Final suggestion for Kindred: mark both sides but link their souls
After discussing with a friend of mine, he helped come up with an edit for my previously suggested change to kindred's marks. Instead of rotating back and forth between sides for marks to force the enemy to invade, we came up with the idea that the same mob on both sides become marked. And if one of them dies, the other loses its mark and Kindred can no longer stack from it.
If the matching buffs are ever not both alive, then it'll simply chose a camp that is. Only the first mark needs to match.
This way, the enemy can still prevent Kindred from getting a mark by killing the mob on their own side, and will succeed in doing so if they rush to it and can clear it faster. But Kindred will be able to get marks without risking death. She may even miss it by a quarter of a second because the enemy cleared theirs just a little faster, but there won't be such a high risk for such a small reward.