I think that totally restoring their stats might be a bit bad, but giving them some of them back would be nice. Maybe having health roughly equal to the average marksman (or, hell, even only roughly equal to the squishier marksmen) without having to have
would be nice. Semi-adequate armor and MR, too. Maybe even having a slightly higher base AD than
would be nice. I get that they can't be allowed to be too powerful, as the nature of their passive allows Kindred to become the strongest force in the game (one-shotting everything that isn't a building at 8000 stacks), but it's just a bit absurd that every single champion in the game has every stat higher than them (obvious exceptions such as base Gnar or Thresh's base armor apply). But to nerf their passive at all would, as of right now, remove their last shred of hope of being viable, unless accompanied by a sizable buff to their stats.
The recent changes to Wolf torturing you their passive marks was nice, and it made things a bit easier on them, but they're still kinda screwed, unless they're either lucky or against a braindead jungler.