Can't seem to improve in pullups

Hey guys, I've been doing pullups for a while now. I can't seem to go over 12x in a set. I tried applying tips from Athleanx and other popular youtubers, but I just can't pull over the 12x mark, the next set 10x the next 8... and so on. I don't kip or use any momentum at all, just strict full range of motion pullups.

It's been a year now that I'm performing dead hangs, weighted pullups, and negatives beyond 12, but still no good. Is there anything I can do in my training to get over this plateau? I can't believe how other athletes pull up 15 - 20 without breaking a sweat, and here I am falling asleep due to exhaustion after 12 or halfway to 13... Oh, btw I weigh around 74kgs, if that helps.