I'll admit now that I play inefficiently. Or what some would deem inefficiently. I use controller on PC but without the L2+R2/reverse combo. With all the heavensward abilities I considered using it but I just hotbar switch (that's where the inefficiency comes in). You can absolutely fit everything you need on 32 buttons in the classes I tend to play (DRG, WHM, WAR).
It actually makes sense (to me) for WHM and WAR, because I have healer/tank stuff on the first and DPS stuff on the second. As DRG though, there are times I've thought I really should start using the additional button combos rather than hotbar switching. Only because there are (incredibly rare) instances of having to wait an extra move to use an off-GCD move. It doesn't happen often. Prior to HW all the base DRG moves, power ups and off-GCD's fit on one cross hotbar with AoE/ moves you rarely or never use on the second. Since HW I've basically got those and the HW moves on the second hotbar, so when doing 50+ content I have to hotbar switch, but I'm so used to it that it's not an issue.
Also for the record I'm a filthy hotbar cycler, I don't actually manually choose the hotbar when switching. I just make sure I'm limited to two hotbars (the third is locked across all classes for class switching/ mounts/ teleport etc). It's more efficient in battle to press R1 to cycle than it is to hold it in and choose another hotbar.
I wouldn't say the controller is in any way limiting to DPS, ability to heal or ability to tank especially if unlike me you use the additional combo hotbars. Until they release new moves with an expansion and the rotation totally changes, I can't see me changing to KBAM for DRG. The only thing I'd maybe say is that I'm giving myself more work than the role needs to be, but I'm so used to it now that my performance in the role would suffer for quite a while if I re-trained. I may try the additional cross hotbar thing when I start playing again later today since I've been away for two weeks. The way I do it is kind of awkward to explain/ talk about, so I may make a video at some point to show you all what I mean.
For pet-based roles yeah, it really should be KBAM. Not that being top-tier in those classes is impossible with a controller because it's certainly not, it's just a bloody headache for micromanaging the pet (repositioning pets is an absolute pain on controller).