360 rule does not apply to Piezography curves. The Piezography curves with the QTR driver break that rule.
With a normal dithering - there is a lot of paper white that is unprinted. This is the space between dots of ink. This is especially true with low frequency dithering patterns in which a darker ink is made to look lighter by using fewer dots of ink and much more paper white. With Piezography curves, the dithering is always at high frequencies and there is never space between dots. Ever.
The space between dots is being printed in Piezography with detail. It is not being printed with a normal driver output and yes you are right - with color work anything over 360dpi is simply wasted.
But, not so with Piezography.
But resizing a file does nothing to take advantage of that.
You have to have optical resolution to take advantage of it.
At Cone Editions we drum scan medium and large format film at super high resolution.
For my own work I use a Sony A7R and enjoy more pixels...
The new Canon would not be wasted on Piezography - but you would want to have really decent glass.