Do B787 pilots get paid more than the A320 pilots on the basis that it is a larger aircraft ? That would tend to support the argument for a pay increase.
However, does a B787-10 pilot get more than a B787-8 pilot ? That would tend to counter the argument.
Unfortunately, there is enough commonality between the A320 and A321 for management to claim that it’s simply a variation and not a different type. A320 to A330 would be a different matter.