However i want to ask a couple questions;
1.Do you speak of a hypothesis in any way or a well established and final conclusion about Slavic languages?
2.I want to see your data on which you are so sure,i.e river names or whatever arguments you have about the Proto-Slavic homeland? since you are the one that you insist on that.
I do not see how you would come to a different conclusion. The data mainly comes from the lexicon and the phonetic evolution of the Slavic languages.
Again please bring the arguments you have about the Proto-Slavic homeland since you insist on that.
First, you had Balto-Slavic linguistic unity at some point (in the iron age, e.g. metallurgical terminology). You have common lexicon, common phonology. More importantly, Proto-Slavic before the Germanic loanwords entered the stock is very close to to reconstructed Proto-Balto-Slavic. You also had language contact between early Balto-Slavic and speakers of Uralic languages, more precisely the Finnic branch, because Finnic borrowed some terminology from Balto-Slavic.
Second, there's the terminology for the environment: Slavic borrowed the word for 'beech' (buk) from Germanic (the Slavic words adhere to Grimm's Law, and the Germanic *ō was rendered as *ū into Proto-Slavic), which suggests that Slavic speakers originated in an area were this type of tree did not grow, and entered at a later point into a (Germanic-speaking) area where it grew. In contrast, you have a common Balto-Slavic word for 'birch' (shared actually with Germanic, again note how the Germanic word adheres to Grimm's Law while the Balto-Slavic words are palatalized), which does grow in northeastern Europe, but does not grow in the steppe.
Another key issue that I see is the fact that the early Slavs were polytheistic, and that again, you can tie up strong links and parallels with the Balts.
As i said i can not be conclusive in this and in anyway i will not bring such conclusion,however the Slavic languages are tight to the greater Indo-European family so it all depends..
What cought my attention was this so shouldn't be left unanswered.
If I'd follow your ideas (Slavic languages originate on the Balkans), I would not expect such a close relationship between Baltic and Slavic (Slavic should be closer with Albanian or maybe even Greek - at least from areal contact - than with Baltic). I would expect unanimously Slavic place names, personal names and deity names from the Roman period. I would expect Latin loanwords to be much more extensive (as is the case in Albanian), and I would expect older and earlier Greek loanwords (and not just Church related terminology from medieval Greek - which again, is the case in Albanian). Since none of this is the case (all of that taken together accounts for a solid, testable hypothesis), I can only conclude that Slavic languages originally were far away from the Balkans and arrived there only during the Migration Period.
A fundamental proposition of historical anthropology is that human genes, language, and culture represent distinct systems of inheritance. The three systems are distinct and have no necessary relationship because each bears a different relation to population history.
If you think that you can write a history on linguistic hypothesis,including migrations,then please you or other linguist that insist on that,wrote a Indo-European history,so all of us Indo-Europeans can have a common history at least we gonna have something in common and then to all other according to our respective languages.
Which hypothesis you are going to use?
After all everything starts and ends with a language.
Like I said before, some form of movement is necessary to explain the situation: either you argue for a movement of peoples (aka demic diffusion), or you can argue for cultural diffusion. What you can't do, in my opinion, is ad-hoc argue "migration period never existed" and leave it altogether unexplained where the Slavic languages come from or why we do not have a record of them from the Balkans in the Roman period.