Agreed. I have a similar configuration, and opponents will typically burn their Oblivian Rings or other removal on the Champion.  In my deck, I make the Champion the threat, and then switch to Exalted attacks once I have numerous Exalted buffs on the field.

If the goal is to play Sublime Archangel (and other Exalteds) the +1 buff offered by the Cathedral is less important than it would be if you didn't have those other Exalted buffs.  While you currently are Mono White, using Cavern would not only protect the named type from counterspells, but would also allow you to play splashes of color (so long as the creatures are of the type named when Cavern of Souls enters the battlefield). Thus, Knight of Infamy could appear without needing to risk too many mana of the alternate color.