That is why I put "" around 'breakpoints'. My personal opinion is that there are no breakpoints, simple as that, each point is worth the same.
However others could consider there to be breakpoints like such as I described. If you for example would go from 4.51s to 4.49s in for example thecks simulations, you would notice a big difference, since it is in all sense and purposes a breakpoint for patchwerk 1.5s swing timer fights. But as you mentioned, boss abilities hold this to be false in real virtual world tanking.