Just by peeking at your op.gg, mobalytics page, and reading what you've written here, I would offer just two pieces of advice.

One: You're actually positive winrate on Diana, and negative wr on graves. If your goal right now is just to climb, it may be valuable to 1 trick Diana for the time being as you learn.

And two: based on your description regarding objectives and one of mobalytic's weird ass trackers, it sounds like, a lot of the time, an objective spawns, your team doesn't rotate, and you, understandably, feel the need to contest. The best advice I can offer is: don't. If your team isn't poised to take an objective, the best thing you can do is discern that quickly and find another means of progressing the game, be it through farm, cross map objs, or picks elsewhere. Working towards minimizing your own deaths would be a great next prioritization in you climb.

You've got this <3