My issue with repurposing current abilities is how limiting the design would need to be. Take the Holy example. To make it a gain in singletarget, it needs to deal more than 310 potency to be 'better than Glare'. 2x damage is 300 so even that isn't enough. you'd have to do 'increases potency by 200' for example, making it 350. It's centered on the player, meaning you could be out of range when you need to use it. Some would say that's a place for optimization, Ren 'fixed' the optimization's element out of it by saying it could gain the ability to be selftargeted or centered on the enemy. A solution to the solution, adding more dev time into the pipeline.

But the main concern is how rigid it would make the rotation. Take the '3 Glare, 1 Holy, repeat' we've seen given as an example. This makes it functionally a 1112 combo. There's no nuance, no deviation, any required healing just bumps the rest of the combo along, making it 11RR12 for example (R being Rapture). It's a solution, yes, but it's a very bland solution, and if we only had one chance to 'get this right', I don't believe this would be enough. I'd take the change if it were made, as 'its better than nothing'. But at this point, the bar is on the ground (or buried in it), so 'getting over the bar' is not a difficult task.

Also, it'd potentially cause issues with weave timings. Holy is a 2.5s cast still, if you can believe that. They could reduce it's cast time to 1.5s like the rest, but again, it'd be another change added on to create a solution for the solution, not the original problem. I can see the merit in trying to keep 'additional buttons' down on some classes, like SCH is absolutely rammed with buttons atm. But at the same time, it's SE's fault we're in the situation where 'button bloat' is a concern, because they have given us so many buttons that we're drowning in OGCDs. So I don't really take 'but the hotbar space' as a be-all-end-all condition to respect, as things can be consolidated to free up space for the sake of making better design. And if it IS a condition to respect, I don't consider 32 to be the 'sacred number', but 36, given that SE regularly exceeds 32 on many jobs at the moment. In which case, WHM for example, with some smart consolidations, can have up to 7 'free spaces' to work with IIRC