Fang's of the Boowolf takes a dump on linear res. Prespic is also a huge advantage when you have over 100 linear res w/ 50%. I'd like to think that is common in PvP with a Osamodas in Otomai.
I don't know what all this whatnot is about. The best class to use to kill an Osa is a Sadida. Always was. It's their spell mechanics. Sacriers also generally can pick off some also but I feel as though that's heavily dependent on the Osa's resistance setup vs them and if the Sacrier is able to hit 3 times with Sunshade or 2. As for Intel Enus, I can spam more summons than they generally can kill.
The primary reason an Osamoda is powerful is the utility it has to reduce damage inherently by distributing summons, unbewitching, mediocre/subpar map control and AP reduction. Their advantage isn't in the early game but mid to late. While I was PvPing during Head Hunter, I often had to take 30%+ damage to my health before my summons really started to overwhelm. Controlling those in whatever way possible is how you win.