@mchill
Kasparov makes the point that no one who reaches GM level today will have done so without having trained against an engine. This has two effects on human-to-human GM play.
Suppose that all candidate GMs had learned from the same human GM above them; the candidates' play would tend to resemble the other candidates' play, with only very minor differences, right? Same here, with GMs all having trained against the same engines.
Secondly, engines exploit material advantages with extraordinary efficiency, and therefore to prevail against an engine requires a certain style of play which avoids risk. Human GMs who have trained against engines have developed the same cautiousness about getting into tactically risky positions against other humans.
The result is that there is a group of players at the top with nearly identical skill sets. This is very different to the days when someone, such as Rubinstein or Reti for example, could lock himself into a room with a stack of chess books, play
himself the necessary ten-thousand times to get the skills, and emerge onto the world stage at GM level with a very distinctive style all his own.