This video should give you the answer

https://youtu.be/1Taz5Fq-WzM 

This video should give you the answer

https://youtu.be/1Taz5Fq-WzM 

Video doesn't answer it entirely, as not every debuff is cast by an attack. If an attack is a weak attack, zero percent chance to land the debuff. Thus debuffs that are tied to an attack have a 35% reduction in being able to land.

However debuffs that arent tied to an attack cannot be a weak attack, therefor these are unaffected. (for example lyssandras cooldown reduction ability doesnt deal damage, therefor is unaffected by affinity)

debuffs vs affinities is only a problem when hitting weak. then no debuff can be applied

a weak hit is a hit on a stronger affinity (35% chance to hit weak, no amount of c rate can negate that 35%)

for example a blue hitting a red