That's a good question- and I'm afraid I don't know! I do know that the really exaggerated wasp-waisting became less important as engines increased in power and our understanding of supersonic aerodynamics got better (you may note it's not really a thing nowadays) so it's entirely possible the Soviets skipped over the period it was a must-have design characteristic, or found a different way to apply the area rule- it's not an area of particular expertise for me, so this is just conjecture, but I'd be interested in seeing if anyone more on the engineering side of things knew more!
