I think the problem with talent is people have different definitions, it's sort of a gray area.
What is required to be a great tennis player? athleticism, eye-hand coordination (timing the ball), ability to concentrate, 'feel', mental strength, fitness.
Some think the mental aspect is not a talent, some think it is. Is ability to time the ball a talent but not ability to concentrate? why not? because people think 'timing' is innate but concentration is not? this is an endless debate..
To me, 'talent' is overrated, way overrated. People love to speak of guys like Nalbandian, Marcelo Rios and Safin as underdeveloped talent, as if they could, in theory, accomplish what Federer, Nadal, Djokovic have because of their abundant talent. The problem, is, what talent did they have exactly? and what did they not have? Here's the debate that matters. Let's focus on Marcelo Rios and Nallbandian. Both hit the ball cleanly and had 'feel', they could time the ball well. Okay, is that it? Seems we put a lot of weight on two things - eye-hand coordination (ability to time ball) and 'feel', ability to hit the ball in different ways. Okay, now, what about ability to concentrate point in point out? This is not a talent? We could argue, they lacked this talent. Now could they hit every shot as they pleased? not really, in the case of Nalbandian, his serve was mediocre, on most days. So, if he was so talented, why couldn't he just serve like Sampras, Federer? same for Rios. Isn't this a lack of talent?
Athleticism is a huge factor as-well. Is it any coincidence that Federer, Djokovic, Nadal are 3 of the greatest athletes tennis has ever known? super fast, agile, coordinated, balanced? Look around, the others, with exception of Monfils, don't quite measure up. It doesn't matter how well you can time and feel the ball, if you lack athleticism, you are at a disadvantage. Could've Rios or Nalbandian truly won 15-20 majors if they would've trained as hard and would've been as mentally strong? I doubt it, the big 3 win many matches, purely on their athleticism. When a player has length, speed and is agile/balanced, they can get to balls easier, they can position themselves better for shots, time and time again. This gives the more athletic player a massive advantage over a player who can feel/time ball better, over course of a match. How good is it to be able to time/feel ball better if you can't quite reach shots or position yourself as well as the more athletic player? Rios and Nalbandian didn't have quite the same athleticism.. They could've done more than what they did but i would not bet my money on them winning 15-20 slams just because they were aesthetically pleasing and timed the ball well.
Safin is one who had athleticism, a big serve and could hit the ball cleanly but he wasn't as agile and fast as big 3 either and he was a heavier guy, not sure he could've won 15-20 slams either. I saw him face off against Federer and lose more often than not to him, the AO was just one match and he barely won that one.
The issue i have with 'talent' is that when someone says player A had more 'talent' than player B, they imply player A could've accomplished more, fitness/mental strength/work ethic held constant. I disagree.... First and foremost, player B may have underappreciated talents other than just 'timing/feeling' the ball and be a better overall athlete. People tend to bucket a specific skill as talent yet ignore others...