I don't think that it is possible to make direct comparisons between players today and those of 25 years ago let alone 50 years back. It is a totally different game.
In the 1960s, a lot of players were essentially part-time, even many in the top two divisions. Current players are far fitter and benefit from developments in sports science.
Harry Dowd worked as a plumber throughout his career as did Tom Finney of Preston. My PE teacher from school was Trevor Porteous, full back for Stockport County. He left the school only when he was appointed player-manager at County. We also had Ray Wood, goalkeeper for United (until replaced by Harry Gregg) as part-time games teacher. He was in the Munich air crash. He had moved to Huddersfield by then.
The other factor was the state of pitches back then. Most were essentially mud baths apart from the first few weeks of the season.
Put the best teams from the 1960s against the best teams today, on current pitches, and there would no contest. I would be less sure what would happen if you could transport the current teams back on play of pitches like the Baseball Ground in Derby.
Also you need to factor changes in the standards of refereeing. The likes of Norman Hunter could not play today as they did back them without getting red cards every match.
In tactical terms City under Mercer and Allison did anticipate some of Guardiola's thinking. Glyn Pardoe, a midfielder, played a hybrid full back/midfield role not unlike that of Delph and Zinchenko. However in most cases direct comparison is not vald.