Anything that has to run through 2 layers of RNG to trigger is probably not going to be very strong, and this is essentially the case here, as well. Having 2 extra seconds of disable is nice, but the cost of leaving it up to even more chance and reducing probability by half just makes this a worse version of No Egrets.
I respectfully disagree, for a few reasons:
1: Filia is better able to rush up, attack, and retreat than parasoul. She can avoid a lot of blockbusters by being just too fast.
2: Filia has a lot more lighter hits: that RNG is EASY to make when you use drill tempered, gregor samson, hairball, or even the average combo.
3: those extra 2 seconds mean a LOT when the first hit in a combo is the one that connects. I want to complete my combo and have time for another without blockbuster punishment afterwards.
Although I will admit that I'm not very good with parasoul, so perhaps I am biased... but of the 2, I can keep enemies locked with my frosty perfectly fine.
Edit here:
I should probably say it like this: for filia, how many hits I use on average make her crit multiple times each combo. And a lot of special moves that are good for filia have multiple small hits. If you are optimizing her crit % and moves like you would no egrets, I think that it is easily worth having a chance to disable for the 150% stun time. No egrets, however, probably would not enjoy that same limitation because. Those extra 2 seconds to not tag out or use a BB3 can be vital in some fights