The gamara there is about being makriv all at once. The Rosh chulin 100a uses this to learn to taaruvos but we only go with that Rosh when there is hefsed.
My recollection about that CD is that it it's differentiating between the movement allowing bitul or a true parish but I may be getting confused since that is along the lines of R Chaim.
It’s 10 kohanim and they are being makriv each separately. Not quite sure it’s the same. The Rosh is zoning in on the fact that it doesn’t revert to being kavua.
I don’t think think the Rosh applies at all when bittul isn’t possible because of a דבר חשוב. His shita is based on נתנפך להיתר which doesn’t apply here. That is what the CD says too, that you can’t eat them all because there is a דבר חשוב which isn’t battul. I’d like to know if the sources you quoted say explicitly otherwise.
(I may be totally mistaken, checked it quickly on this it what it seemed to me. If I’m wrong LMK)