The Draco standard

[Robert Vermaat]

That reminds me of not only excluding the obvious, but even changing it.

I know of a similar occasion, where a modern researcher changed things a bit. This was about the plumbata as mention in the Strategikon. Translating the text to a singular, soldiers of Maurikios sudenly were armed with only one weapon instead of more in one quiver, and next thing you know is that the text is used to prove the evolution of the plumbata from a throwing dart to a mace!
Kolias, Taxiarchis G. (1988): Die Keule und der Streitkolben, in: Byzantinische Waffen. Ein Beitrag zur byzantinischen Waffenkunde, Von den Anfängen bis zur lateinischen Eroberung, Byzantina Vindobonensia, vol. 17 (Wien), pp. 173-184.

What we have to guard against is a kind of perverse logic that says that, if the ancient sources do not mention it, it must be so because they must have regarded it as too obvious to mention.

We have be wary of that indeed, which is why I don't support such perverse logic. But we still have to take into account that the possibility exists. If we exclude that possibility, we are forced to take each text literally. For instance, the Strategikon mentions cavalry far more than it does infantry. Should we conclude that the infantry was a minority on the batlefield and of no consequence? Or is it possible that the text concentrates on cavalry because this is where the innovations were concentrated? Whereas the infantry had not been subject to such innovations?

Now, I would take the opposite view: that the serpent-tail was adopted because, like flags, pennons, streamers, etc., it caught the wind and spread out, making it more conspicuous as a rallying point in battle. If (and, in my opinion, in the absence of confirmatory evidence, it is a pretty big 'if') the draco acquired an additional function as a windsock, this would have come later.

Eagles never had serpent tails, nor did a vexillum develop into a battle standard with a streaming tail. Neither do Celtic, Germanic, persian battle standards which arer solid objects without streamers.
No, can't follow you there, because if this was a logical development we would see many more battle standards with streamers or tails, and we don't, at least not in this period. The 'draco' therefore, in my opinion at least, is far more likely to have been originally something 'with a streaming tail' than something that aquired this in order to function better.