No, the TMRCA was 2000 years ago, +- a few hundred. Some scholars place the ethnogenesis of proto-Slavs around 200 bc. That's the closest event relevant to the TMRCA i can think of. Some place it much earlier though.
you are forgetting west and east Slavs spread i2a-din with them too.
Even if the "i2a-din people" were originally non-Slavic they:
1) lived right next to Polesia
2) were completely absorbed by early Slavs
3) mixed so thouroughly with early Slavs that wherever Slavs went, they brought i2a-din with them.
or it was just Slavs.
Serbs have around 35% i2a-din, but 25% of the very young subclade I-PH908. take that away, and there is 10% i2a-din, which is quite low even for a lot of east and west Slavic regions. We have a low i2a-din variance, in other words.
This is the rule number one of haplogroups. More important than anyhing else.

