The Mig 25 was designed to counter the B-70 Valkyrie bomber that was never built. Later on they added look down shoot down radar, a "wizzo" weapons officer, and long range air to air missles copied from the US Phoenix AAM they bought from the Iranians after the Shah's fall, and came up with the Mig 31. It actually is a pretty effective platform with high speed and a good range and electronics (possibly French) but rotten in a dog fight. The SU26-35's are a tough customer. Have directable thrust which gives them outstanding agility. Probably better than the F15 performance wise, but not the F22. The SU 24 has proven to be F-16 fodder. The Russians use it like the US Air Force did the F-111.