We are not talking about bowlers here
You realize how illogical it sounds? Modern batsmen are supposedly inferior to the batsmen of the past because they are playing in easier conditions, but modern bowlers are not superior to the bowlers of the past because they are playing in tougher conditions.
The best ODI batsmen of that era will not average 80 today, and the best batsmen of today would not have averaged 20 in that era. It is all about adapting to the conditions and the top players adapt that is why they are among the top players.
If you take a modern batsman, put him in a time machine and take him to the 70s and 80s, he might not be used to the lighter bats and big boundaries. However, he will adapt. Similarly, if you put a player from the 70s and 80s in a time machine and bring him to 2017, he will not click immediately but he will eventually adapt as well.
Batsmen of that era had advantages that modern batsmen don't. The fielding standards in that era were poor and batsmen got a lot of singles and doubles that they would not have got today. In addition, the introduction of the TV umpire meant that the benefit of doubt for batsmen decreased.
In the past, when the umpires gave run out calls on naked eye, they made massive blunders and batsmen would often be adjudged run out when he was deep in his crease. Similarly, the introduction of the DRS has furthered reduced the benefit of doubt for batsmen. In the past, the batsmen had the luxury of no Hot Spot and Snicko, and let's not even talk about the biased umpiring.
The key term is adaption. If batting in this era is a piece of cake as some people make it sound, you would not have only a handful of elite batsmen. Yes there are good batsmen and very good batsmen, but very few elite batsmen. These elite batsmen - and Kohli is one of them - would be elite in any era because of their ability to adapt to the conditions better than their peers. Similarly, elite batsmen of the 70s and 80s would be elite today if they were exposed to modern conditions and standards of cricket.
Hence, it is futile to make cross-era comparisons. The fact is that an ATG would be an ATG in any era, and that is why he is an ATG and not just a good player.