I would like to agree with you, but where is that written in NEC 334.80?
To be honest, I don't even see any "spacing" requirements listed in 310.15 for raceways, single or multiconductor cables, AC or MC, even where bundled or installed in lengths over 24-inches.
All I see is that the spacing, of whatever amount you begin with, must be maintained throughout the run, even when making bends.
On the upside though, for the purpose of derating in Table 310.15[B]2,a, the neutral conductors of 3-wire multiwire branch circuits are not counted as a current carrying conductors, which may help keep the wire count down in some instances.
