What is your goal climb?
I think it’s silly to pick exercises you can’t do well, but it’s equally silly to do something that is very easy for you. I would scale the exercises back until you are doing good form rather than progressing with “ok” form. Along those lines, I would rule out L-sits. If you can’t do pushups properly, what about doing weighted plank?
As for step ups, I would imagine you could get a lot out of smaller step ups/downs with weight and you could work up to bigger steps. But again, along those lines, you’ll want to keep good form to avoid getting hurt. You might also want to do some PT exercises for your knees to help reduce flare ups as you progress.