Furthermore, if we require a static context to compare players across eras, how accurately can we go back? The early 00s or late 90s, maybe? The game is always changing....but it is gradual, and over many years. We also have players who spanned quite different eras - like Federer, Agassi, Santoro, Connors, Rosewall, etc.
Think how quickly we can get back to in time: Roger Federer played Andre Agassi, who played Jimmy Connors, who played Pancho Gonzales, who played ...etc.
The game changes, but so do the players - who adapt to new contexts. Rod Laver went from dominating the relatively small but potent pool of the Pro Tour to winning all four Slams in the first full year of the Open Era, and remained an elite player for another half decade or so. Peak Laver might not have done well in the more powerful game of the 1980s to present, but he was great in the context he played in and was able to adapt to new contexts (we cannot say the same for the much -overrated Roy Emerson, who flopped in the Open Era).