First off thanks to Emperor1997 for the hint with the negative honor trait, I had been up to attempt 101 from the 70 I talked about in my initial post and as he had the -1 honor trait I captured and executed him without losing any of my traits, good thing to know that I can do this now with any unhonorable prisoner lord.
So the next one took me 45 attempts, then I was 15 attempts into the recent one when I read Zorion_no's last post and I remembered a surgeon perk that might be the problem, it's "Doctors Oath - Medicine recovery chance applies to enemies too", my Surgeon is level 134 and she has that perk active, I'm not sure, but if that perk lowers the probability of dying on the battlefield, then my dumb ass created this struggle himself. I set my surgeons party role to "none" now and after that it only took me 7 more attempts until the next dude died in battle. I will test this a little more now, if it means I always got to switch her clan role before those death-battles then that's quite the hassle, but if it helps then whatever. I think I play on easy btw.
Those auto-generated clan successors are a joke too, I also saw many of them wearing female clothes and roaming the map with tiny parties because their skills are non-existent, I also made another thread some days ago pointing that out because instead of a clan being destroyed upon me killing the last member, a new member in a dress spawned out of nowhere and kept the clan alive.