It's an interesting theory.
But your assumed proto Slavs would plot like a banana on the PCA (your three black circles) which is per se unlikeley. A "normal" heterogeneity would go in all directions and just make the a basically "round" area on the plot bigger. At least in tendency.
Doubtless a number of individuals that you add to the assumed by others as proto Slav groups are mixed. Individuals like Av1 and RISE569 (Early Czech) can be completely discarded. Arbitrary slavic-like individuals from Scandinavia as well. There is also no serious cause for assuming all Krakauer Berg individuals (they are very late) to be proto Slavic in genetics, just the moste extreme ones could be thought of. So these individuals could be thought of to be proto Slavic:
Av2
KRA001
KRA009
KRA011
POH13
POH28
Likely also
VK2020 (Zehden, East Brandenburg)
Sunghir6 (may be questioned depending on whether Stearsolina's objections are applicable or not)
We will then have abt. that area that I circled in red here as proto Slavic. And it has some heterogeneity.
https://i.imgur.com/Nebb4hJ.jpg
Your left black circle I assume are southern admixtured proto Slavs and the green area are people that are not just admixed with Germanics like from Kovalevko, but also a lot with all that indigenous (likely Germanisised in 600 AD) pre Germanic people that lived in Bohemia and Pannonia. Consider that all that dark admixture in Bohemians, Upper Saxons, Thuringians and Southern Saxony-Anhaltians is neither from early Celts, nor from early Germanics, nor from proto Slavs, but from the prior LBK-influenced population. This easily explains why that admixture resulting in the green area from a proto Slav perspective - as circled in red above - is not just in the direction of Kovalevko Goths (or Burgundians). Because of the obvious prior population in these areas that were not that early Germanic-like as Kovalevko Goths your left black circle is even disproved to be proto Slavic. Why. Because from that position the green fied just show an admixture in the direction of Kovalevko Goths.
My conclusion: I agree to your middle and right black circle to be proto Slavic and I add abt. half of your red area to that, resulting in my red circle. I reject your left black cirlce as part of proto Slavs with the aforementioned motivation. The various admixture directions of the Proto slavs, resulting in the various known samples, are marked with red arrows. (Note that I do basically agree to your center and right black line as an admixture direction, just not to the left one.)
Is that a reasonable point of view?