I created a map of CTS9320 based on some projects from Family Tree DNA.
View attachment 11462
https://imgur.com/5BzrRBW
Its distribution reminds me of both I-M423 and R1a-M458. Its origin must have been somewhere along the Northwest Coast of the Black Sea and it could have been common among the Dacians. I believe that the Goths first brought CTS9320 into South Balkans and North Italy and then the early Slavs carried more of it into Balkans and Central Europe.
I was thinking about the same for a while and I think your thinking is not far from the truth...
This particular subclade(but not only this one) looks like it might have to do a lot of things with the Pontic steppe and the north Black Sea coast.
As such, I am tempted to connect it with the Scythians and also because we have a confirmed E-CTS1273 Scythian from Moldova.
But what is a Scythian?
Looking at all these 'Scythian' samples and how different autosomally they were, it seems that the only Scythian about them was the culture they accepted. So in other words, these Moldavian Scythians were people native to the area and assimilated into the Scythian society.
Probably all of this wouldn't have been so important if it wasn't for the Slavs and most importantly the South Slavs!
Because one striking feature that distinguishes the South Slavs from the other groups of Slavs is the higher incidence of haplogroup E related subclades among the former but not quite. The Ukrainians and the Carpathian Slavs known as Rusyns also have a lot of E related subclades among them, around 10% if I am not mistaken.
Furthermore, the Northern Slavs were never known as Slavs or Sclaveni among their neighbors but were known as 'Wends', 'Veneti' 'Veni' etc.
The term 'Sclaveni' was only used by the Byzantines first and later on in history it became an accepted term for all Slavic speakers.
In this regard, am on the opinion that the term 'Sclaveni' is only valid for the South Slavs as they were the first recorded with that name.
Therefore, we have now two variables that distinguishes the South Slavs from the rest, first is the higher incidence of E related subclades and the second is the name...
Now you probably already know what I am thinking about so here is some food for thought...
Could the name 'Sclaveni' as they were recorded by the Byzantines, be a sum of the names 'S(a)ka' as for Scythians and 'Veni' as for Wends?
We don't know how the Scythians were calling themselves but we do know that many people including the ancient Persians have recorded them as 'Saka'!
For the Achamenids, there were three types of Scythians: the Saka tayai paradraya ("beyond the sea", presumably between the Greeks and the Thracians on the Western side of the Black Sea)...
Even the Albanians and the Romanians are using the term 'Shka' when talking about their Slavic neighbors which could be related to Scythians or S(a)ka!
As for the Wends, the term 'Veneti' or 'Veni' were largely in use by the ancient historians and the Finns are still calling their Slavic neighbors as 'Veni'!