I would also point out that for a considerable part of his early career Karpov and Kasparov were in a class of their own. In 1991 Kramnik would have only been 16. So if Kasparov played in a tournament without karpov - yes he was likely to win.
IMO their is much more competition at the very top tournaments, that Carlsen has to deal with.
Carlsen can obviously not be compared to Kasparov with regards to career achievements when he is 22, but it is interesting to compare his recent tournaments with Kasparov’s from the middle of his reign. That this is even possible to do says something about how good Carlsen’s results have been lately.
The last three years Carlsen played these tournaments:
2010 Nanjing 1st +4-0=6 2901
2010 London 1st +4-2=1 2815
2011 Wijk 3rd +5-2=6 2815
2011 Bazna 1st +3-0=7 2853
2011 Biel 1st +5-1=4 2833
2011 Sao Paulo/Bilbao 1st +3-1=6 2842
2011 Tal Memorial 1st +2-0=7 2849
2011 London 3rd +3-0=5 2875
2012 Wijk 2nd +4-1=8 2830
2012 Tal Memorial 1st +2-0=7 2848
2012 Biel 2nd +4-0=6 2878
2012 Grand Slam final 1st +4-1=5 2876
2012 London 1st +5-0=3 2994
2013 Wijk 1st +7-0=6 2930
2013 Candidates 1st +5-2=7 2850
2013 Stavanger 2nd +3-1=5 2834
2013 Tal Memorial 2nd +3-1=5 2846
2013 Sinquefield Cup 1st +3-0=3 2966
18 tournaments: 12 first places, 4 second places and 2 third places for Carlsen.
In 1991-96 Kasparov also played 18 (individual) tournaments:
1991 Linares 2nd +6-1=6
1991 Max Euwe Memorial 3rd +2-0=7
1991 Tilburg 1st +7-1=6
1991 Reggio Emilia 2nd +3-1=5
1992 Linares 1st +7-0=6
1992 Dortmund 1st +5-2=2
1993 Linares 1st +7-0=6
1994 Linares 2nd +6-2=5
1994 Max Euwe Memorial 1st +3-1=2
1994 Novgorod 1st +4-0=6
1994 Horgen 1st +6-0=5
1995 Riga 1st +5-0=5
1995 Max Euwe Memorial 2nd +3-2=1
1995 Novgorod 1st +4-0=5
1995 Horgen 5th +1-1=8
1996 Max Euwe Memorial 1st +5-1=3
1996 Dos Hermanas 3rd +3-1=5
1996 Las Palmas 1st +3-0=7
18 tournaments: 11 first places, 4 second places, 2 third places (1 fifth) for Kasparov.
One remarkable thing with Carlsen’s results is that his worst TPR in these three years has been good enough for clear first on the rating list. Kasparov had better periods than 1991-96, but those were not bad years for him while Carlsen still is quite young. Comparing Carlsen’s results with “weaker” World Champions rather than with the maybe greatest player ever would make them look even more impressive.