Nah, Shinryu ex does not need a nerf. It's a good fight, and should stay as it is. In a few month it will be a faceroll anyways. so keep it as it is for the time being

That said, if even I, who is a pretty casual player (meaning I don't raid in a static, don't do savage etc...) can manage to learn and kill this thing with pugs, then farm it successfully and without any remarkable problems, it's a pretty doable fight.
Of course I can relate to the bad feeling of getting bad parties in pf, but the only thing you can do about it is leave the party if you notice that the poeple are for example not concentrated enough or die constantly in p1 in a p3 training or kill party.
I don't wanna say that you have to be an a-hole or mean...no way. I don't support this. But be consequent. That's all.