GunshipDemocracy wrote:@flaming and @Viktor
Thanks again so requirements for Army and ASF are so different that one set of missiles cannot do?
They probably can but why should they?
They already have 2 different families of systems; the Buk/Kub familly and the S-300 familly; the former going back to the 60s and the later to the 80s.
Since their inception these families have grown and evolved and been forked off, and as of 2015 both represent a wide range of different systems with different capabilities optimized for different roles.
The role for Army mobile air defence is best fulfilled by the Buk-M2/Buk-M3
The role for Army mobile ABM defence is best fulfilled by the S-300VM (S-300V4)
The role for Air Force mobile medium-range air defence is best fulfilled by the S-350
Why should they kill off one of these families after all the investment put into them? As GarryB mentions, both have enough orders/demand (inc. export demand) to make them economical. So if they can both be supported, they should.
Otherwise you'd end up trying to fulfil the long-range defence role with a Buk-type vehicle, while having S-300 type chassis's trying to keep up with armour formations in the field, firing at threats on the move - and it's clear that it just won't work very well.
You really do need both families; and since you do - then you might as well take advantage of that and pick and match the variants from either of the 2 familiies that you feel are optimal in a particular role.