Sadly a lot of westerners believe the weapons the Soviets introduce are simply copies of western systems and they don't develop anything themselves.
Because of this some think there is no competition in weapons development and a design bureau is simply designated the task of making a particular platform... so for instance the reason the MiG-29 and Su-27 look similar is because they were planned from the start to be copy mixes of Hornet/Falcon/Eagle/Tomcat aircraft.
The reality is of course there was plenty of competition for programmes in the Soviet Union... sometimes copies were included and sometimes copies were the only option.
Their first air to air missiles were complex and not super effective... the AA-1 alkali still lives on in the form of the AS-7 and AS-10 and AS-12 air to surface missiles in the form of the Kh-23 and then the modular Kh-25 missile system.
The first Soviet air to air missile needed a rear facing antenna to receive commands via simple datalink, so the rocket propulsion had to be moved from the rear to the sides like most ATGMs, and if you cracked open a missile it was a complex mixture of wiring and systems all mixed together.
When they first got their hands on a Sidewinder they were shocked at how simple and basic it was... from front to rear it had sections... seeker in the nose, then the control surfaces and their drive mechanisms, then the warhead and guidance electronics and then the solid rocket motor and then the tail fins at the very rear.
The didn't have time to absorb the concept of modular design and construction... it allows motor upgrades and seeker upgrades and changes in aerodynamics much easier than with their old model custom designed complex method... so rather than wait for the concept of modular simple design to flow through their design bureaus and wait for a brand new all Soviet weapon, they just took what was interesting from the US design.
Soviet rocket motors were better so they used one of their own design and their seekers were better so they also used that, and of course they used their own warhead and fusing, but the layout and modularity of the design was copied, as was the gyros which were tiny in comparison to Soviet models and very simple but effective.
The concept of modularity is what they really copied and took it rather further than the Americans ever did.... case in point the R-27 family of missiles is enormous and offers several types of motor and seeker with the same basic aerodynamics.
They chose to copy then to get something totally radical and new into service quickly so it could be used, but replacement missiles based on the new design philosophy soon followed.
Actually in competition for the replacement for the R-23/24 for the MiG-23 on the MiG-29 and Su-27, there was a Sparrow like missile with the same fin layout using similar systems and parts and offering the same performance. It failed miserably against the R-27 family, but they would have happily adopted it if it had outperformed the alternative.
Of course everyone does that, but the west has the advantage of time... something might be in service in the Soviet Union for ten years before good pictures of it appear in the west... so when the BMP appeared and the west decided to start copying the idea of an IFV, the US introduced the Bradley and the UK introduced the Warrior... both basically copies of the BMP-2. The F-15 was needed urgently and was supposed to counter the misunderstood MiG-25 so to start with the copied the basic layout to start with. the list is actually rather long... auto grenade launchers, assault rifles, weapon families (ie rifle, LMG, assault rifle, SMG etc based on the same design...) And now it is designated marksmen rifles (SVD) and of course RPG launchers... of course the west tends to take it too far... with their DMRs expected to kill to 1,000m or something silly like that... and their RPGs looking like they were made by Mattel... for GI Joe...