I've had inspectors claim that when you over size the neutral then you expect it to be a current carrying conductor. On a 3-phase panel that's now 4 current carrying conductors so the conductors are derated to 80%. I'll point to them where it states that neutrals are exempt and they'll just say it doesn't apply when I oversize the neutral. Just so you know.
In this case since 100% of loads are non-linear the neutral is already a CCC
(4) Neutral Conductor.
(a) A neutral conductor that carries only the unbalanced
current from other conductors of the same circuit
shall not be required to be counted when applying the provisions
of 310.15(B)(2)(a).
(b) In a 3-wire circuit consisting of two phase conductors
and the neutral conductor of a 4-wire, 3-phase, wyeconnected
system, a common conductor carries approximately
the same current as the line-to-neutral load currents
of the other conductors and shall be counted when applying
the provisions of 310.15(B)(2)(a).
(c) On a 4-wire, 3-phase wye circuit where the major
portion of the load consists of nonlinear loads, harmonic currents
are present in the neutral conductor; the neutral conductor
shall therefore be considered a current-carrying conductor.