Could a Foxbat shoot down an SR-71? The latter is like 0.6 Mach faster. The former was built out of steel, had an underpowered radar, couldn’t climb as high as a Blackbird and carried AA-6’s, which would have to lock and hit their target before the solid motors ran out [1]. To my knowledge the MiG-25’s claim to fame is shooting down an F-15 in the Gulf War.
In any case, it’s clearly been worth it. The B-2, B-21 and RQ-180, to say nothing of our (sc)ramjet research derives directly from the Blackbird.