IMO .... Yep...they copy stuff well ;-) (see B-29 opps TU-4)
Serioulsy, the Soviets "were" very handy at "Making Do" with what they had. The Mig-25 used highly advanced "tube" manufacturing to withstand high altitude temperatures. A Very nifty problem detection system for gound maintenance crews and where aerodynamics weren't important, exposed rivets. And if the missles and guns didn't kill ya...the radar could ;-) Shielding? whats that?
Its low alt performance couldn't touch an F-15, however once it hit 40,000+ feet it could out perform the F15 hands down. Of course, this is what it was designed for, B-52 bomber interception.
The dominance factor of Jet Fighters these days has very little to do with the Jets Dog Fighting (that is last resort tactic these days) but more to do with the Missles, on-board avionics and counter measures. Being able to track 8+ separate targets and shoot them down from 80 miles out ( see F-14 Tomcat) was why the Soviets built so damn many Migs. They figured if they launched 10 v 1 they would win the 2 v 1 that was left.
"Quantity has a quality all its own." - Stalin
China aided them greatly in the 80's when the Sino-Soviet realations reached a point that allowed some exchanges of technologies. With the technilogical advances in the computer control systems and avionics the Soviet aircraft became much more capable with features like thrust vectoring, computer aided flight controls and multi-target fire control systems.
The biggest difference in mindsets was: The Soviets built for special purposes the US started building for Multi-Purpose-Use (see defunct F-20 and F-35 Joint Strike Fighter....argh ;-( )
Since the last Soviet/Russian planes manufactured were back in the 90's there have been no significant advances in last 10 years. Now the competition is between the US and the EU ( see EuroFighter ). Which fighter is more generic THAT is the question? ;-P
Softail.