I can assure you that the slowing down, in my case, is not a product of easing off, but tiring out. I’m not talking about a crazy sprint or anything.
An example: 90 RPM for the many first minutes. Then - for various reasons - I might fall to 87, which is fine for some minutes, but really is below my optimal cadence. If i was to accelerate up 90 again very late in the test, it would ruin the rest of the test, so a quick shift up the cassette brings me back to 90.
So basically it is not about getting a break but getting speed back into legs. And as I mentioned earlier, I’d prefer if the whole thing happened in a split second.
I would actually argue that trying to accelerate without changing gears would be the counter productive thing to do.