Things like completion % and TD/INT ratio have changed massively over the last 30 years and saying ZW is better at those than guys 40 years ago is more a reflection of how the game has changed - how those stats are more emphasised now and how the game has changed to free up the offense more.
John Elway had a career 62.1 completion rate (never a season over 65.4%) and just under a career 2:1 TD/INT ratio.
Davis Mills, the current Stanford QB, has a career 65.5% completion rate and a 2.25:1 TD/INT ration.
Clearly Davis Mills should knock Elway off Stanford's Mt Rushmore. But then again, Elway would have probably been knocked off by KJ Costello. And yet there's a reason Elway was one of those guys seen as a generational no-doubt QB (John Elway, Peyton Manning, Andrew Luck, Trevor Lawrence are the guys viewed that way coming out)