First,
Happy New Year to Orthodox Christians who practice their religion by Julian calendar .
it is irrelevant in which direction was spread originally
On contrary, I find that information about directions of spreading very important.
and on haplogroup I map it is place on Caspian sea shores from which spread goes towards west and north west with west end finishing in Kuban region...well, try to look on place of Serboi and imagine what would happen with spread if they were migrating towards west and nortwest and than look map again...
By logic of shapes, and isohypses gradation, it looks like west to east direction. It just flows nicely and in 2-3 visible steps towards mouth of Volga. This shape also gradually shapes through centuries. This is not coincidental. At least not by this visual data from map. The question is in shape logic not a haplogroup type.
Concerning haplotype I:
Don't forget that almost all Alans - Sarmatians residing in that area were eradicated by Tamerlan, eccept those that retreated to mountains.
What we see are nowadays data about people living on that place. The question is how much of Alanian I is in them, since this part of the Russian plane was a home of so many nations, very much different. Also it could be Russian population gradually moving in vast uninhabited land after Tamerlan slaughtering population of planes.
Mostly Ossetes are claiming Alanian descent today. Their country is officially known as North Ossetia-Alania. For your theory to work, where big numbers of I2a2 came from Alans, there should be at least equal G among them in places where they supposedly came to. In case of Serbia and Croatia there are about 0,9-2% of
G. There should be proportionaly lower percent of I2a2 coming from Alans.
G spread is more logical to mouth of Volga, also since that of
I looks it came from west ( could be Russian ). Also waves of G in Serboi area (Alan tribe), carry more potent
frequency range of G (Frequency range: 0% to 31.7%) than I (Frequency range: 0% to 22.6%). They should be in proportion of 26 G to 18 I, in waves projecting on that area nowadays.
Only if we accept those I to be there after Tamerlan destruction of Alania. In fact G waves also look like repopulation of Alan areas from G carriers, after Tamerlan. Only this G moves in logical settlement areas for G.
Also migration of large numbers of people (exodus like?) to territories of nowadays Poland and Germany (White Croatia and White Srebia) can not be attributed to warlike, warrior elite on horseback like Alans. Large numbers of people does not go along with warriors, since they are mostly going on foot and with children, women, their possessions and cattle, and no warrior would like to be slowed by them. To propose great numbers that could be relevant comparing to indigenous population of I2a2 from Balkans, came from Alan is not possible (by my opinion). It looks more like warriors on horseback came to indigenous R1a of Poland and Germany and settled among them. Maybe some I2a2 were alrady there among the R1a.
It is estimated that there were no more than 35000 Alan warriors in Europe. Even big numbers of Mongols and Huns have left no relevant genetic traces. Very small part of Europe population have this genetic imprint (except Hungary).
Today there is no certain genetic trace that could be attributed solely to Alans. It is speculated though, that G2a is most probable carrier. In fact, I am connected genetically of course, along with some other people to, so far, only relevant bones of
alleged Sarmatian origin warriors (two of them) buried in Merrovingian Germany of 7th century together with four warriors of R1b. These alleged Sarmation origin warriors are buried according to Sarmatian customs with horse skull and horse feet. I am actually more closely related to these two people, than I am related to some of nowadays living g2a carriers from Europe, even after 1300 years.
Madyars of Caucasus have over 90% of G1.
They differ so much from Madyars of Balkans, but name couldn't be coincidence.
There is Jasi minority from Hungaria, who came from Alania prior to or after Tamerlan. Jasi or Osi is Georgian name for Ossetes. They still have Caucasian heritage.