Given how the Cleansing Wars lasted thousands of years there may be any number of champions that failed in that period. There may also be secret champions, or agents with other blessings that operated further afield or in a similar position just on different continents. It may also be considered there could have been a large segment of “neutral” champions that did not aid the rebellion against Rajaat nor oppose it and instead adopted what is most likely a position of petty warlordism abroad. Or perhaps exist in a tributary status, not explicit vassals as the Tableland SMs appeared to be.
Some quick ideas about why any given CoR/SM may have been absent from Ur-Draxa (beyond insanity like Daskinor): Other powerful servants of Rajaat emerge from the Black and begin laying waste, forcing these other SM to deal with these incursions personally. Either building on that or in isolate, perhaps there are other sites of power important to maintaining Rajaat’s prison, and if they abandon these posts Rajaat can escape fully. Perhaps that is why only the Tableland SM seem to have such a free hand - living directly in Borys’ shadow may relieve them of this personal responsibility. There is some indication such wards exist though this is speculative on my part, in that the Cerulean Storm seems to be stuck in Ur-Draxa. Though that could just be Tithian being tied to the Black Sphere now, I proffer there may exist wards to contain and/or exclude beings of extreme power within the Valley of Dust and Fire.
Also OP, I love the idea of an Inca SM, and Pachacuti makes a great framework for that. Some of the Incan cultural elements are really strong for use in a setting with undead (Kaisharga Mallqui anyone?). If you’re not familiar with them, you may want to check out the Dominions series as there is a faction “Nazca” which is an Inca-themed nation of winged people some of the units, commanders, heroes, and pretenders may give some inspiration