Daniel
I exaggerate(but just a bit) and I rely on my opinions on my knowledge and ability to integrate and interpret that knowledge. They are opinions, not facts, obviously.
Of course, players do not hit 3-irons as close as wedges, but they hit them pretty damn near as close (relative to the past), and certainly they hit them higher and softer than any golden age architect could have ever imagined.
Re poor old Walter Hagen, whom I do NOT mean to belittle, but just use as an example (I could have used anybody from his era, including Bobby Jones), I have no specific knowledge about his skills other than the scores which he recorded in major championships. I base my opinions about Hagen's skills relative to today's players on those facts, as well as pictures I have seen of his and others from that era's swings, which are (obviously) pre-modern and thus not as totoally effective as today's swings. I also base it on what I know and beleive about other players in other sports, some with more convinciton than others, namely:
--that Bill Tilden could not get a game off of any of today's top tennis players. (I played a lot of tennis, I;ve sen the films, and this one is a no-brainer).
--that Jesse Owens could not make today's Olympic teams (another no-brainer--look up the numbers)
--that Johnny Weissmuller could not make today's women's Olypmic team! (look it up, it's a no-brainer too)
--that Babe Ruth might be a struggling DHer, but not much more (harder to prove, but I am increasingly awed at the physical skill of today's baseball players, inccluding pitchers)
--that Bob Cousy probably couldn't play NBA ball these days (again hard to prove, but I'n not sure his one-hand set shot would be of much use these days).
I will admit that golf always has been a sport at which the less fit and less athletically gifted can excel, and also one at which older people can continue to compete with younger ones for a longer time, due to its particular characteristics and requirements. However, even that is changing now that better athletes are coming into the sport, and physical strength is becoming a greater element of the modern player's game.
Daniel, there is a lot of research out these days on how people learn and achieve that makes it very clear that for people of similar inherent talent, the cumulative number of repetitiions of skills determines long term performance. Thus the chess player who starts at age 3 is more likely to become a grandmaster than the one that starts at 8. The swimmer who starts competing and training at 5 is more likely to be an Olympic medal winner than one who starts at 11, and so forth. All other things being equal, of course.
I would be astonished to learn that Hagen, and Jones,and Sarazen, etc. had trained any where nearly as hard, for nearly as long as have Woods, Duval, Mickelson, etc. Including recovery shots. I am reliably told by people who have seen him practice that Woods can do things with a golf ball that Hagen could never have dreamed of. Also remember that 50-80 years ago the greens that the older players were recovering to stimped out at 4-5. It's a lot easier to get a recovery shot to stick on a slow green.
......I just wonder where Sarazen's famous 4-wood would have ended up if the 15th green at Augusta were as firm and fast as it is today? Maybe in the cup again, but maybe, just maybe, through the green into the water.........
Let me make one more caveat. I am comparing how I imagine these older athletes played, based on slim records and old video clips, vs. what I see with my eyes today. How those old athletes played was determined, in large part, but the amount and quality of training they undertook. I think one of the reasons for my opinions about their relative abilities is based on the fact that they did not trian as long and as hard as today's athletes. I am fully willing to concede that if Bobby Jones had trained as much at golf as Tiger has from age 3 onward, through his playing career, he could have been as good an athlete and golfer as Tiger was. However, he didn't and he wasn't. IMHO.
I marvel at the skills of all the old players, in all sports. I am a sports junkie and I have played several sports at reasonably high levels. I am, however, also an analyst and a realist and I do not really get anything other than bar room-level satisfaction from trying to debate whether or not Jack Johnson would beat Rocky Marciano, or Jacques Plante be able to stop Mario Lemieux one-on-one, or Walter Hagen beat Joe Durant at match play.
I've got some rose colored glasses in my desk somewhere, but I haven't worn them for some time.
Hey, here's an idea that just came to me! Honestly. I think as I write 
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How about doing a match play comparison of Jones vs. Woods at Merion, as it was in 1930, and as Jones played on that day and as Tiger plays today? Does anybody have the knowledge and patience to try that one? Does anybody out there think that Jones would have had anything other than a small statistical chance in that match?
Daniel, I love the past. I am of it and I learn a lot about it and from it, every day. However, I am also in the present, I am also forced to deal with the future, and I try to live my life and form my opinions based on a healthy balance of those three incontrovertible facts.
All the best
Rich