OOOPS THIS IS WRONG.
Turns out that any tree structure with N leaves is total data size O(N), not O(N log N). However, there is a constant multiplier on N relative to an array of N entries.
For a binary tree, the multiplier is 2.0. For a tree where nodes have 4 children, the multiplier is 4/3, which honestly is pretty dang close to 1 (this is the same as mipmaps for 2d textures, they only add 33.33% more vram use; every 4 pixels in the original texture is 1 pixel in the next-smaller mipmap, which is equivalent to grouping 4 leaves in a single parent node, have I ever mentioned that I am an indie game dev wannabe who got suckered into buying Bitcoin).
So yes a CTV tree is more expensive in data size due to the above constant multiplier, plus the necessary overhead of using P2SH/P2WSH/P2TR, but is O(N) on the number of leaves, and increasing the fanout gets it closer to the case of “publish all the outputs”. Hmmm.