It is indeed claimed that a russian, Pyotr Ufimtsev, made the theoretical models for a stealthy design that are still used today.
Strangely enough, he developed his theories in the 1960’s while the development of the first stealth aircraft, the SR-71, satrted in the late 1950’s.
Well, the vertical thrust vectoring system of the Yak is very different from the Harrier approach.
One could even claim that the F-35 is copying the thrust vectoring system of the yak-38.
But I don’t believe all too much of these “copy” claims.
I don’t believe that a company such as sukhoi would eb able to design something like the f-27 after decades of only copying designs;
Of course, there are only so many solutions to a particular technical problems and it is very likely that at a given time and technological state of play, people will come up with similar solutions.
The Mig-17 first flew in 1950 three years after the F-86 first flew. Plenty of time to copy especially if you already have spies in the US
Admittedly not the most striking example, but militaries have copied each other since human history began
The Mig 17 is a continuation of the Mig 15 design, slightly longer and with a wing leading edge with two different angles.
the mig 15 flew first in 1947.
The design would continue leading to the mig 19 with two engines
Mig 15-17 used radial engines, backwards developed from the rolls royce nene
the Mig 19 used axial engines, that were designed using the german jumo (me-262) as basis
It was the unexplicable decision from the UK government to donate some engines to Stalin that allowed Klimov
With superbolic exageration, one could consider the Mig 17 to be a predecessor of planes like the F-111, or SU-24 with movable wings 
As far as I know the mig 17 was the first plane to combine two different angles for the leading edge of the wing. Someone may just have thought… what if…
We have a great saying for this case:
You have to make the sign of the cross if you’re seeing things
Having the same criteria usually result in the same design. It is not that unexpected. Also, if something is proven to be a success, why don’t you follow?
It was an arm race after all, taking whatever can save you time of developing. As say people constantly use what work for their criteria, that are already proven, and refile it into their design. It’s more like learning that copying. Look at how most of the car on the street are all in a similar shape or form. Every time someone break the ice, people will learn from it and result in similar designs.
The early single engine jets are all similar like that regardless of their origin. Many of the single engine jet have single intake at the nose, which is later find to be not that great, with the later of its kind is the MIG-21, with the spike for radar and slow air down, while other move the intake down under the nose.
The wings F-86 are at bottom of the fuselage, the Mig-15/17 has wings at mid fuselage, that alone would change the calculation for high speed flight and structural design. The Soviet jet fight linage started the MIG-9 and Yak-15, which might look similar to the F84F, but its design is more closely resemble to some post war Mig-3 prototype.
The MiG-25 has 2 engines, 2 air intakes under the wings and wings closes to the top of the fuselage. While it looks like the F111, the wings are more alike to MIG-21. Even the west was impressed by Mig-25’s performance, despite its many flaws, and designed later aircraft with experience taken from it. This design then latter appear on many of the western aircraft.
P/s: The SR-71 was an attempt, but it was not as sophisticated like what Ufimtsev developed. The sharp, form and material of it was still a test. Most of SR-71 stealth is still flight high and far from the radar.
When the MiG -29 came out everybody started pissing and moaning about “Oh, they copied this…” , “They copied that…”… An aeronautical engineer brought up the point, " The laws of Physics do not have nationality or political ideology. If you want an aircraft to perform a particular task there are only so many ways design it."