MiG-21, MiG-23, and MiG-27s were single engine fighters and USSR produced them by the masses and used extensively. MiG-19s, Su-7s, Su-17s, Su-22s, etc were also single engined fighters and mass produced. That puts your assertion as a bold faced lie that Russian engines were unreliable.
IAF has reliability issue with Russian engines.
IN has reliability issue with Russian engines.
CAG has highlighted reliability issue with Russian engines.
Their are countless article on internet highlighted reliability issue with Russian engines. You can Google them.
Crash rate of these mentioned aircraft is very high along with abmissal availability. During that time all engines were bad but as time western engine quality improved astronomically compared to Russian.
Remember MiG-27 crashed in Kargil Conflict due to engine flame-out during attack run. Ground attack aircraft suffering engine flame-out while firing 80 mm rockets or guns is unacceptable.
Buddy stop living in denial.
Again, it is the vast distances of Russia that made the RuAF go for twin engined fighters due to the need to carry more fuel and budget cuts that required less planes. Yet RuAF came up with a 5th generation single engine fighter as well.
Frontline fighter aircraft are not required/expected to travel huge distance hence the word frontline.
Su-75 project is sham. Su-75 primarily designed for export markets and not RuAF. SU-75 came into existence due to failure to Su-57 project. Russians have accepted that no countries are willing to buy their Su57s.
Su-75 is designed to be low cost aircraft for export and is expected to cost US $25–30 million.
On a side-note Su-75 is biggest threat to AMCA.