You're reducing the amount of unique key presses from eight to two, in the case of DRG.
While neither is difficult, I find two buttons far more boring, especially given how frequently your combos are utilized. You will inevitably spam two buttons more than anything else. It may seem irrelevant to you, however I much prefer having different buttons. Since they aren't going to add eight new abilities, it will also reduce the amount of buttons on DRG overall—a job which already has plenty of available space. If I had any confidence this would simply be an option, maybe I'd be more open to it. SE doesn't tend to work that way though.
No. Although, I do not actually want new abilities going into Shadowbringers, personally. Regardless, they can simply upgrade existing ones. There simply isn't a need to add new abilities, especially when things like Piercing Talon still exist.
These are not the same thing. Blood Price cannot even be pressed without Grit nor does there exist a combo sequence. Those shouldn't be separate buttons.
A lot of controller players I know don't have any issues. In fact, my BFF plays BRD, AST and occasionally SCH—jobs far busier than DRG. Not only does she have plenty of space on a controller, she hates the idea of combo consolidation. To quote, "Just upgrade my DoTs and leave my fucking job alone."
Or they upgrade existing abilities like I mentioned previously. Two additional options are to expand the combos so better interact with one another. Say Disembowel combo-ing into Full Thrust triggers a different effect. Another option is to bake new oGCDs behind existing ones with lengthily cooldowns. You don't need to add a new button entirely when Litany sits on a three minute CD and does precisely nothing until its up again. Any of these alternatives accomplishes the same thing without taking away any abilities. Granted, Piercing Talon can still die. I'm also not a fan of Dragon Sight but that's more because macros are awful in this game. Either way, they have plenty of options which don't involve reducing DRG to pressing two buttons more often than not.
That number wouldn't even make up a full percent. You don't design a system around the possibility of someone physically handicapped having difficulties interacting with it because, pragmatically speaking, those types of players are exceedingly rare. Furthermore, you seem to be forgetting the opposition those threads have received every single time. Even on Reddit whenever this gets suggested, it gets shot down.
If there were such an outcry demanding combo consolidation, Yoshida wouldn't have made a point to specifically say they aren't doing it for PvE.