I'm not interested, today, in reading over the entire datasheet. However, a search reveals no reference to lock time, acquisition time, tracking range, lock range, or any other significant parameter used to characterize a genuine PLL. This, apparently, is just a clock synthesizer, probably with the typical lock time of about 2 seconds. While that might be adequate for startup, it's not adequate for switching MCU execution rate to match a synchronous process.

I do this kind of stuff all the time, and, frankly, find this "hand-wave" of yours disengenuous. Do you even know what a PLL is? Have you ever used one, say, in a communication task where the data rate varies slightly? What about where you switch from one data channel to another, at a high rate and have only a finite length of sync field before you start to lose data?

RE