The A321 rate was a shortsighted mistake made years ago. To ward of any possible reduction should the company purchase A319’s, a family rate was agreed upon as they never envisaged we’d get A321’s. Of course, here we are 15 odd years later, with NEO’s instead of a new type and stuck with the Family rate.
As for the 777 rates, it’s a blend between the -200 and -300 rates. With the 787 however, the -10 (currently) has the same MTOW as the -9. Time for ALPA (and by that I mean the collective) to grow a spine and negotiate a new method to calculate fleet pay.