A Van,
Dear Ivan, it may be said that the lady doth protestesth too much.
What you say is plausible but to go on to exonerate the Russians and blame the Ukrainians is too much.
A high altitude SAM is needed by the one in case of attack by the other. To say the rebels don't need it as the Ukrainians only use SU25 is nonsense as they might fly higher. The Russians may pose a high level threat either directly or in support.
So anyone could have done it. The question therefore remains who and why.