The S-400 deal with Russia, comes as a mixed bag with gains at best being political. On balance it would be safe to say that militarily, despite the S-400's formidable capabilities (as advertised) will not translate into a serious game changer on the ground, and its purchase costs may be misleading as its integration may turn it into a white elephant that could bleed the military down the line.
What we need to be clear about is that on paper, the S-400 is a formidable capability against aircraft. It has very long range and ability for extreme manoeuvres, which means