There were lots of guys who hit with topspin back in the 70's..perhaps the difference was that they were not trying to rip the cover off the ball 100pct of the time. I don't see such tremendous athletic supremacy of today's guys over those of generations past. And, there were guys from the 70's/ 80's and 90's who bridged into the more current generations...like Connors, Lendl, Agassi, Sampras. As they aged, their games evolved as did their equipment (aside from Pete, that is). So, I just don't believe this idea that today's guys would completely trample those from generations past. The stroke production is different, perhaps harder, not necessarily superior in results when the end goal is to win points and games. The old counterpunchers, in particular, I think would likely hold their own with superior footspeed and movement. Who was, or ever will be, faster than Borg? Who has the movement and eye/hand coordination of a Connors? Lendl's consistency? Agassi's blistering returns? Very few. these are guys w/very unique attributes that made them successful; same to be said of the top guys today.
The players today, regardless of racquet technology and strings, hit the ball in a fundamentally different way, especially off the fh side. I think the results are significantly superior, so we don't agree there. They generate way more racquet head speed, which results in way more pace and spin. Aside from Borg and Vilas and likely a few others, no one from the 70's was hitting with that kind of spin, which also includes varying amounts of side spin, and Vilas and Borg weren't hitting with the same pace as today's players, even taking the racquets and strings into consideration.
While I never mentioned raw athletic ability, today's players are generally bigger. Modern technique allows these bigger, stronger athletes to take bigger cuts at the ball and still have it land in.
Regarding all the other stuff like eye/hand coordination, foot speed, etc. - of course the best players from years past are equal to today's players. If these players played in the same eras with the same techniques, then things would be interesting. And players from adjacent eras are similar enough to be competitive.
But techniques have advanced IMO. Taking players of similar talent, one using modern technique and one using 70's technique, the modern player wins.
Again, all just my opinion.