Very interesting elaboration, I'm really fascinated, Bernhard

But my confusion even intensifies.

Meter in our terminology is essentially regular, rhythm irregular.
....
What parts of the pulse can best be used to maintain or alter a tempo?
The offbeat parts, for example beats 2 and 4 in 4/4; 2 and 3 in ¾.
When pulse may be used to alter the tempo, how could he say, meter is essentally regular?
I don't think, there is something like a regular pulse at all.
There is a regular
counting, but this doesn't mean, that the tempo of counting is fixed, it's only the
numbers (the words) we count, that are fixed.
Perhaps you will climb the barricades, but I'm really convinced:
Every single note has its own tempoThere are even single notes, which will get slower or faster in itself.
Measure and counting are for differenciating the
function of any note
Notes on beat 1 of the measure are like the tonica in the cadenza.
Upbeats, which can be a single note, but also groups of notes, in some cases almost the whole measure, sometimes even 2 or more measures, are like the dominant in the cadenza.
I don't be convinced of this pulse-thing, so far as it stands for something other than
counting, which never should be mechanical or unflexible.