No doubt 4th gen fighters are tons safer than 2 or even 3rd mainly with the digitization of flight controls etc.... also I didn't say they were not safe.. just much harder to fly. Like anything it all depends on the driver and the experience.
I've heard MiG 29 is not easy to fly for the novice either but once mastered it becomes very easy.
Let's just say I wouldn't want to fly one one even if given a chance for free HOWEVER I would a PAK FA because I think it's much easier to fly.
It depends in the variant, and aircraft it self, the MiG-21 has been built in China under different guises, they call it J-7 until very recently, but Russia stopped MiG-21 production in the late 1970s or early 1980s.
India has given a bad reputation to the MiG-21 because they built theirs in the 1980s, they have not the best maintenance.
The MiG-23s were expensive to maintain, and not that different from a MiG-21 so not many air forces kept them after the fall of the Soviet lead block.
Most of the stories related to the flying qualities of these aircraft come from export models and from the 1980s, but a MiG-21 was comparable to the Mirage III, the Israelis said it was not worse, even the Americans knew it was like a F-104.
The Israelis said the MiG-23 was a F-4E equivalent, the Americans flew and even older version, the MiG-23MS, and later they received MiG-23ML from Germany,.
Germany flew analog MiG-29A (export version) built in the late 1980s. These MiG-29s were equivalent to a F-15A, so when they compared the Mig-29 they flew F-18As which were newer in avionics, but Russia was flying MiG-29Ms (prototypes) and Su-27s, which were equivalent to F-18As.
So to be honest it depends in which version and aircraft, i am sure a modern J-7 is more or less as safe as a F-16, and the modern MiG-35 as safe as a F-22.
But old MIGs well no one want to fly them
