Kindred can stack indefinitely so they scale into late game well, they have utility with a decent ult, they have mobility with a WQ and they have great sustain.
Vayne is easy to abuse early and mid game, is poor when behind, but much like Fiora a Vayne is just a ticking time bomb as long as they now not to be in the frontline all the time. BoRK, Runaan's and Deaths' Dance or Bloodthirster makes a late game Vayne a monster as long as they can position well.
Late game Kindreds can also shred tanks but can also run tanky. So where Vayne can be deleted the moment she is out of place and/or cc'd, Kindred can shred tanks, take more damage, play riskier for the same rewards AND has a "you can't kill me needle needle nee" ult in case of emergency for whoever stands in it all while having innate life steal on her own.