>>17438192>>17439054>>17439388 I think that overally he has not enough body on himself to excuse the removal of that waist disc. Plus, it sort of makes sense as some sort of regressed remnant from his Kirlia stage.
Personally, I think that removal of that 'detail' should become a design uplift for his hypothetical Mega evolution - as it would only make sense for it to become bulkier in appearance and thus allow Gallade to lose this piece of geometry without making him look like a stick figure.