Raid buffs are a design constraint. Without it, you can place your burst window wherever you feel like it. It's a skill check, but it naturally has a convergent effect on job and fight design. But that's a necessary evil, if you want to be able to reward skill over freestyle gameplay.

Raid buffs don't necessarily need to be player generated. You can just as easily have a scripted window where a boss takes more damage. This is actually a harder check, because players have no control over the timing and no way of adapting to problems on the fly (i.e. player deaths). The easiest check of all is if you have a single player that dictates the timing of the raid window, because you can essentially place it wherever you want on the fly. It also means that you could potentially run a full freestyle group without buffs, if all jobs are balanced around rDPS. The middle ground is the system we currently have (most jobs provide raid buffs, but individually they are all weaker and comp independent).

Raid buffs can't be asynchronous, because jobs that align their buffs more conveniently are preferentially picked. Given the choice, why would I bring a job with 90s raid buffs when everyone else has buffs on multiples of 60s?

Who gets the privilege of bringing the raid buff is less of an factor than you think it is, because everything gets balanced around rDPS. If anything, we've seen that jobs that focused on personal damage output like SAM and BLM have had preferential treatment over other jobs this expansion. They are generally on the higher end of the rDPS scale, despite also contributing more damage than other jobs under raid buffs (and the latter has not been accounted for in rDPS balance). If VPR ends up bringing a self-only buff, it's likely going to end up in a very good place, similar to these two. It actually works to your favor, if anything, to let someone else bring the raid buff.

Bottom line is that the current system has drawbacks, but there are plenty of ways that you can make the existing system worse.