Angra Mainyu is not only the weak being in the Grail, it is the amassed mass of prana and collective hatred of humanity thrown unto the monster. If AM is able to materialize, it will not be something similar to avenger at all, rather, having the Greater Grail as a vessel and such massive amounts of prana in reserve, it would pose an extreme threat.
The Materialized Angra Mainyu is pretty much a 'demon'. It is a materialized curse, and one of the most powerful ones ever, since it carries all of the world's evil. It will not only run on prana, but on the curse/negative emotions that it is supposed to represent, and seeing that it is a being on the scale of the world, that danger is massive.
Primate Murder has been stated to be Dead Apostle Ancestor N.1, but you have to recall that rankings isn't entirely descriptive of power. While there is a certain correlation, the ranking of the Dead Apostle Ancestors is based on their threat towards Humanity/the Church. Since Primate Murder is a monster created by Gaia to wipe out humans, and has absolute power over them, it makes a lot of sense that it is at spot N.1, but that doesn't mean that it is the most powerful of the Dead Apostle Ancestors. That rank should rather belong to ORT, theoretically.
Remember that ORT is the strongest one from Mercury, and is reputably one of the strongest Aristoteles when it comes to Attacking-levels. In comparison, Primate Murder does not qualify as Type-Gaia (we have Archetype Gaia in the Melty Blood Series), and its rule does not extend over beings alien from humanity/from being primates.
Thus, ORT is certainly superior to Primate Murder. If the two clashed, all the chances are towards Type-Mercury's side.
As for Angra Mainyu versus Primate Murder, it is possible that things could go either way... but as ORT itself is a being alien of any 'human' concept, I do not think that corruption will do much against it.
In the end:
ORT is supreme.