Makes you wonder why they stopped making them and didn't bother making any other really fast planes...
Possibly because the SR-71 and family were so mind bogglingly expensive that even the US couldn't afford to operate them and kept cancelling them and then putting them back into service and then cancelling them.
If they were paid for out of the USAF budget they wouldn't exist... it is not an accident they were run by the CIA like the U-2 was.
Developed means putting into service, so no... they didn't develop a better interceptor than the MiG-25 let alone the MiG-31... the F-14 was a frankensteins monster based on the F-111 which as its designation suggests was supposed to be a carrier based fighter but was way too heavy.
Its radar and heavy long range AAM eventually evolved into the F-14 and Phoenix... the missile was better but the radar was inferior to the set fitted to the MiG-31.
The YF-12 can reach mach 3.3, while the MiG-31 2.8. It had better energy retention with the delta wings too. Its only disadvantage over the MiG-31 was slightly lower payload and not enough space for a large radome.
To be fair it was a proposal that never achieved the performance claims attributed to it... had they built it it would have sucked funds from more important projects and not really made the US any safer.
The Russians will have learned quite a bit from their scramjet experience and the aerodynamics of the plane will be aiming a bit higher than just Mach 3 I suspect.
The physical shape of the SR-71 seriously limited its height performance capabilities... otherwise it would be an obvious candidate to break some of the records the MiG-31 set regarding ceiling.