@Viscacha, I just answered the question but didn't intend to qulalify the usefulness of this in solution
I'm absolutely with you on that point. Time critical tasks in the single digit µs range will most likely give you flaky results under different µC load scenarios.
Alone the interrupt latency due to multi level indirection imposed by the framwork will give you a minimum bias of 1..5µs while "raw HW" interrupts should be executed in well under 1µs (more like a few dozen to hundred ns).
But the "OS" and "cloud connection" are nowhere near that kind of time critiality where a few dozend µs (or even ms) will play any role whatsoever.
I doubt that this ISR alone could cause any trouble with the cloud connection.