They've been trying to keep the button count within 2 XHB sets, probably so they fit within the XHB and WXHB, which is 32 buttons. It's what had them merge Minor Archana and Lord/Lady on AST (which was a mistake they never fixed).
I use controller too, but for comfort I usually have my bars set up so set 1&2 is for single target and 3&4 are for multi target for most jobs. There's a lot of redundancy, especially in set 2 and 4.

At any rate I'm leaning in favor of the combined buttons.

At first I thought we'd lose branching combos to it, but after thinking about it for a while that's not really true. We've even seen Viper manage it in the last PLL.

Take WAR's combo, for example. Heavy Swing, Maim, and Storm's Path can be merged into one button, and Storm's Eye can still exist as a separate button, cutting the combo down to 2 buttons from 4. Same can be done with NIN's

SAM's Hakaze could turn into Yukikaze, while they have two separate buttons for Jinpu>Gekko and Shifu>Kasha, cutting buttons down from 6 to 3.