Safety, if shield(2) gets up the only 100% known way to break it is pets, and of all the pets smn happens to give buffs and enmity free/tp free damage, so it's the obvious choice.
A lot of speculation on how to break the second shield last time but nothing really concrete, And then sirens blessing is subtle blow, that's perfect for reducing shield chance.
I think that it's just a really ridiculously high phalanx, like 10k so that's why anni crits go through and pacts easily clear that, but underbuffed and undergeared players think it's pets only, but again no real proof of it. Easy enough to test trueflight power creep is WAY higher than it was 2 years ago and gives static numbers.
I was messing around with the very easy version, granted I am sure its mechanics may be quite a bit different, but I was winning w/ NIN GEO BRD, and some trusts, cant remember which exactly, sylvie, ulmia, and koru-moru, most likely.
My strat was to go in, do NQ buffs, kill all the imps, once they were dead his shield dropped and he would take damage. So at that point I would apply my 10 minute (based on non 1hr JAs) version of zerg buffs and try and kill him as fast as possible.
A couple of runs he reapplied his shield after I had killed the imps, but soon after it would wear off again.
So, the reason I quoted, I agree that it may be a phalanx, and obviously it gets much more potent depending on difficulty.
But I was breaking the shield in VE w/ just katanas and Ku spam. dunno if that is helpful lol.