Vexilifer with or without animal skin?

[Paullus Scipio]

It seems to me that much of this debate revolves around an inherent notion we in modern societies have about the concept of uniforms

True !'uniformity' in the sense of 'identical' is a product of the industrial age. As can be seen by Roman helmets, of which there are so many types, 'uniformity' in the Ancient simply meant 'everyone has a helmet, sword and shield ( of some sort or another)'

It seems to me that the evidence we have does not suggest that a pattern exists

........except that the pattern I originally set out holds true for the period between, say, Augustus and Trajan, which is the period we have most iconographic evidence for (which is why it is the most popular with re-enactors, too, of course! )

do not known what the disks on vexilia actually mean, or if whether the hand at the top actually represents the maniple).

...actually, in the period under discussion, discs don't appear on Vexilla, but you are quite right - no-one has been able to definitely decipher their meaning on signa, despite many theories. The manus idea on the other hand is so likely as to be almost certainly correct. ( Manus/hand symbolised 'handful'/maniple)

So it's something like an acting post rather than anything truly formal?

Yes, again for the period under discussion a vexillation was a detachment from a parent unit of varying size.