[Mod note: Moving this discussion with zanipolo from the Dedicated Haplogroup Pages thread to the Paleolithic Remnants thread...]
Your understanding of the temporal aspect is a bit off here. I'm only suggesting that our best guess for where I2b-ADR was located 6000 years ago is in NE Italy, based on its modern distribution. That's a long time before things like East Germanic migrations. It is more likely a Cardium Pottery relic or something. We have very few samples, and I'm sort of assuming that the diversity is going to be highest in NE Italy, as we have a sample or two from there IIRC, despite it being a very thinly sampled area... suggesting a higher frequency there which may correspond with higher diversity. I'm definitely willing to revisit I2b-ADR as more comes in.
Keep in mind that new I2b is not closely related to old I2b. I2b-ADR is actually more closely related to my subclade, I2c. Understanding where I2b originated is important for anchoring I2c, but it's a bit too distant to have it inform our understanding of I2a2.
I don't know what you mean, "morphed." The whole point of my map was to include all the little clades as well, so that we can better understand the picture 6000 years ago. After that, some subclades got lucky and expanded (I2a1a, I2a1b1a, I1...) and some remained bottlenecked (I2b, I2c-C, I2a1*-Tibor...). The small ones don't really inform our understanding of things like Classical and Medieval migrations, which seems to be your purpose. But they give us an understanding of the origin of their relative clades, and a better picture of Haplogroup I as a whole.
The diversity of I2b-ADR, even though it is a small clade, is too high for that. Although not exceptionally diverse, it beats some much larger clades, including I2c-B and I think I2a-Din-S, which nobody would suggest that about.