The Germans' filioque

I have read SteVen Runciman so I am here for the re-read. I'm getting a handle on how filioque entered Rome. Despite Chalcedon's dyotheletism, in its Greek creed, using a Greek term for "proceeds"; it never thought to clarify the mechanic with the addition of a new word. It seems that foreigners forced it upon us in the West.

Stephen II and Leo III were the Roman Bishops during a fateful time in European and Byzantine history/es. Carolus Magnus was uniting the West; Constantine V was consolidating the East. Over Church affairs both the adventurer and the emperor were meddlers, and both were iconoclasts. So the Papacy of this time didn't have great choices. Constantine wasn't helping the West, so - by default - Leo III ended up crowning Charles as "Holy Roman Emperor". This was annoying to the Greeks but, well; there wasn't much those Greeks could do about it.

I find interesting that it was German saeculars like Charles who insisted on the old Toledan filioque to be inserted: first in the "Athanasian" Creed, then into the "Nicene" (really Chalcedonian) Creed. Contemporary Greek saeculars like Heraclius were more like Theodosius II or Constantius, big on unitarianism, one way or another.

At the Vatican, Leo III himself didn't want filioque and received complaints, from Jerusalem no less. Later John VIII would accept that this was provocative to Greeks, with whom he wanted better relations. The Theophylacts, for what they were worth, which was little, followed John here; Runciman sees them as a second Byzantine Papacy in practice.

So, why did the Franks, other Germans, and various pro-German Popes insist on filioque, and impose it upon our (version of) the Church?

I think it might be that although the German kings were meddlers, they were preëmptive meddlers. The Germans didn't think they were as powerful as Heraclius, able to take the rôle of Father over the Church as Son. (They'd be proven right as the hillfort came back into fashion.) They noticed that it was the Bishop of Rome taking that title Papa. The Germans would not be chained to a new Empire at the Vatican. Especially not if the Vatican was itself answering to near-alien Constantinople.

It was vital to Carolingian Civilisation that the Spirit not flow from the Father alone. And no, the per filium proposal was no compromise.