Honestly, Kindred has always been unplayable. They've never really had a good spot in the meta other than her release when she was completely broken. Currently, she's a late game hyper carry who can seriously kite some people. The issue is, getting to that late game power spike.
Kindred has a really high skill cap, meaning that people must seriously practice and main them if you want to get anywhere other than mid-game with them.
Your suggested change to the passive sounds nice, but it essentially allows them to roam freely whenever they want to get a mark, therefore making them nearly impossible to counter. Riot loves counterplay in champs, and aside from being a squishy adc-jungler, Kindred only has their marks.
If you still want to play Kindred, try coordinating with your bot lane to let you come in for frequent ganks whenever you can mark a champion, securing an easy stack.