I have sparse memory of Lendl (he retired shortly after I began to watch tennis
), but for the little I remember, he looked more like a defender with good power, than our today average power baseliner.
Agassi arrived in the late 80's, but didn't reach #1 by then ; idem for Becker ; same for Muster : his best years have been, by far, in the 90's ; they were the early signs of the incoming new era, along some fellow players.
None of the players who have dominated the 80's (ie: McEnroy, Borg, Connors, etc...) can be seen as today standard of modern tennis players (for the best or the worst, I guess
I watched once the final of RG'83, who had seen Noah winning against Wilander. The speed of ball looked like amateurish level, compared to what we have seen in the past 20 years...
Courier fought for the #1 ranking against... Edberg..! A kind of player that almost totally disappeared since then (only very talented one in the early 2000's similar was Rafter).
And then later on against Agassi & Sampras, the best symbols of the 90's.
Courier was the 1st #1 that bashed (almost) everything coming at him. And then he slightly lowered down, as more & more new players were bashing better, stronger & longer than him.
So if there's 1 player that can represent the arrival of our modern era, I think it's really Courier.
A finer (and way longer analysis) of the Top #10 every year should likely confirm that...