First, the Su-57 would have to locate the systems, and secondly the Su-57 is at risk of being shot down by other AA systems. With the inability to conduct precision airstrikes, the Russians would not be able to prevent the delivery of Western arms to the eastern Ukraine. This in turn could fundamentally change the character of the war.It seems the US will supply Patriot PAC 3 and / or THAAD to the Kiev regime. If they do, I think Russia will use Su-57 to hit them with anti radar missiles. Su-57 has very low RCS and practically impossible to lock on from a long distance away.