They're stuck in a weird balance spot that makes it so if they have enough power to contest early marks, they're OP and they can dominate early and become a late game carry with marks. If they're too weak to get marks, then they die repeatedly and can't do anything for the rest of the game. Unlike other champs, Kindred can't just farm up if behind because the power comes from the marks. I think there has to be a change to the marks themselves to fix it.
They could increase damage to marked enemies (maybe just marked camps), or maybe make enemy jungle marks invisible to the enemy until they gain sight of the marked camps. As another type of buff they could just increase their base armor (that would help A LOT).