Tsonga is bigger, stronger, and clearly a more impressive physical specimen then Pete. He's about 3-4 cm taller and 20-25 lbs larger, most of which is muscle. By athletic, I'm referring to the context of being less of a prototypical athlete rather then their merits as a complete tennis player. If you can't look at these 2 guys and see that then you need glasses. (BTW let us both realize that we're quibbling about 2 guys who are both among the uber elite athletes on the planet

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Seriously, we're judging athleticism based on pictures?
I'm not doubting that Tsonga is athletic, but it's not simply because of his physique. Sure, a bigger, more muscular physique often
correlates with superior athleticism (and we reflexively refer to various muscular types (long and lean like an NBA player, or broad shouldered and strong-legged) as an "athletic" frame), but a certain (athletic-looking) body type doesn't ensure superior athleticism.
What is it to be "athletic"? Track and field is referred to internationally as "Athletics" - What's being tested in track and field - strength, speed, endurance, movement. Those are "athletic" qualities - and people can possess those qualities regardless of how they look. In individual sports, we judge how those qualities are applied in the context of that sport when talking about how this player or that player is naturally athletic.
I know more than a few gym freaks who have supremely "athletic" builds but are actually fairly awful athletes. Sure, they're strong in the immediate context of whatever weightlifting exercise their doing - but their strength doesn't transfer well and doesn't result in a bigger serve or longer pass, for example. Plus, their movement is pretty bad. On the contrary, I've seen plenty of people who don't look so stereotypically athletic who are, indeed, great athletes.
None of this is to say that Tsonga isn't a great tennis athlete. But, to conclude that he's actually a better athlete than Sampras because he has a more stereotypically athletic build is pretty ridiculous. I'm not seeing much difference in power, endurance, movement between the two.