I have read somewhere that the MIG 25 was a bit of a copy of the Canadian Avro which was cancelled due to so many Soviet spies being involved in the program.
Also tho the MIG 25 had an incredible top speed, it was not all that great as a fighter.
It was designed as a pure interceptor. It was immense and not maneuverable, and would have been a poor dogfighter. Its purpose was to intercept high-flying bombers and recon aircraft; really, it was largely a Soviet counter to something like the USAF’s XB-70 Valkyrie, the Mach 3 bomber prototype tested during the ‘60s but abandoned because of the increasing accuracy of SAMs and ICBMs/SLBMs.
The MiG-25 was built to climb rapidly, dash toward a target at Mach 2+, and fire missiles. But it wasn’t until this defection that the West really understood that the MiG-25 wasn’t some kind of air superiority superfighter. The result of the West’s panic over the MiG-25 were the F-14 Tomcat and the F-15 Eagle, both of which (the F-15 especially) were vastly superior air superiority fighters to the Foxbat.