I think the marks have some dual aspect to them. Yes, it sucks that they are only on the enemy side, but they can be used to deceive the enemy as well.
- Camp spaws on bot side, I mark the top enemy. Enemy jungler has to either head towards top, hoping I plan to gank so he can counter gank, or head towards bot and take the mark, hoping I don't gank. So if I have some deep vision and sit around KFC/Wolfs, I know where the enemy is going, and can safely go to the other side.
- Mark an enemy jungle, path my way "falsely" towards him, then when out of vision, go farm the enemy jungler's bot side, or just gank bot. If I show my wool heading top, against a marked enemy, he will probably go towards there as well.
- My mid lane enemy is having a rough time and I am in no position to help but their mid doesn't know that? Mark him and give my mid some breathing room just because the enemy mid will be cautious of a gank.
- The plain old but gold "mark top gank gank bot"
- Mark spawns bot, I mark bot as well, so enemy jg will be "encouraged" to go towards bot side, so I can freely gank mid or top, while he wastes his time waiting for me bot.
Kindred is still an adc, and so she can hurt badly even without marks. A fed Kindred, even without marks is still going to hurt.
Yes, at first I also though about "must get marks", as when I started playing this version of them, I was focusing on the play style of the old ones, but after a bunch of games, and understanding how much impact the mark presence alone has, she feels much more rewarding when played properly.
And don't fool yourself, at most you need 4 marks to be in a good spot, because of the huge 75 range buff. The next marks after that are just icing on the cake. Can you get more? Good. No? No problem. And you also don't need the 4 marks ASAP.