I actually disagree that it's useless at the pinnacle of optimisation because if you're speedrunning and optimising to that degree you take it into account (just like the finer points of LB gen). Whether it matters or not is another thing entirely. Context, as with everything, matters.
Take a fight like Ramuh - as it is both of my healers have grey percentile healing and so do I. This is with overhealing for all 3 players.
My EF overhealed for ~69% last night during our weeklies. I am not changing my FBT timings when our kill times mandate that I rush. But our healers are already doing low %ile healing as it is, they could stand to reduce that even further (in fact, this wasn't our SCH's most heal efficient run, the week before was lower grey healing for her). It didn't change how they healed at all there.
But if we consider a case like Momo opting for a 0 heal GCD speed run of a fight. He absolutely will take it into account, but again whether it matters to that end equation or not remains to be seen. These must all be mapped out. If it helps result in extra potency just from being more efficient with tools, then it will be done.
This doesn't make it something you can reliably lean upon in a more general case. It's nice if it lines up, but if it doesn't, no way in hell is a SMN ever to be expected to shuffled a FBT around in a typical situation just to line the heal up better. Anyone who expects that owes their SMN a better group.