The Primaries were weaker than Anagogic Sorcerers of Rank.  At Shimeh they concealed their presence until the Scarlet Spires had tired themselves out blasting their way into ambush point and then attacked, surrounding the poorly positioned and tired Scarlet Schoolmen.  Elizearas himself holds off two of their most powerful primaries for a while despite tiring his school out and leading them into a killing field.  Shimeh proved not that the Primaries are stronger than Sorcerers of Ranks, but that the difference in strength is far less important than tactics.

As for disguise magic, the Cishaurim were able to enter the Scarlet Spires by stealth and a witch was able to masquerade as a priestess of Yawter.  It clearly exists, with the Cishaurim having the advantage of not having the mark which was why everyone thought the skin spies were theirs.