You have hit the nail on the head. He has been winning Wimbledon at a canter every year not even having to play that well. Whilst Im not saying he doesnt play any attacking shots, its a largely defensive game that relies on errors from his opponents and just wearing them down. Obviously effective but incredibly dull. It just shows what a pathetic era this is.
I doubt he would have won any Wimbledon's on the old fast grass. Wouldn't have had a chance against the grass court specialists of old. The likes of Sampras, Edberg, Becker and Goran.
So Djokovic isn't in the calibre of,
Agassi 1xW & RU, Courier RU, Connors 2xW 4xRU Pioline xRU!
Connors is outlier as he didn't win in the 90s. But he played fast grass. Djokovic volleyed in recent times as well Borg ever did, noted he didn't play 90s but 70/80 grass was faster and more erratic, but the tools where under powered.
End of the day Wimbledon 90s was Sampras and not many player could challenge him in grass in 90s condition including Federer, Borg, Mac, Becker, Edberg, Goran, etc. He was too good for that eras technology and conditions. Agassi as an outlier of 90s is only due to not meeting Sampras, swap 92 & 93 opponents and Agassi wouldn't have a Wim and Courier might have won.
Federer would not have beaten Sampras in 90s conditions either, he nearly beat him on slow grass during poor form with sampras going 5 set against the Mighty Barry Cowan.