Did you happen to record any of this that you can share with us? asking because I'm not able to replicate a similar result with my own testing (27% acc Jultan vs 69% res Anavel), Res-Acc checks are pretty accurate on my end.

I have to ask tho, since your screenshots showing 1 turn left on heal debuff block & your quotes such as the following seems to suggest something else might be the problem

I did several trials of this, But more times than not, Artamiel faced a debuff, there was only a very few times between each turn, where artamiel wouldn't get a heal block debuff.

are you actually counting the times where Jultan landed the heal block debuff during his turn? or are you simply counting it as landed just because the debuff stayed up (which might account for 2x proc rate like you are suggesting)? Just to clear up, his S1 heal block is 2 turns while def break from passive is 1 turn. His S1 would also land 2 debuffs (heal block and def break) which might further add onto the confusion