I'm not that sure Hewitt was inherently more talented. He had exactly two strengths -- legs and head.
He was fast and he could slide towards the ball even on hard courts. He was precocious. He had the focus and maturity to fight for every fifteen very few teenage/early twenties players possess. He hit the ground running with a winner mentality. Plenty of grit, plenty of resilience.
The rest of his repertoire couldn't really be considered weapons. Yes, he had good passing shots, yes, he had a good lob, yes, he had some finesse, but it's not like he was indescribably otherworldly, and the new string technology+slower courts rendered these qualities nearly useless once most top cats dropped the S&V nonsense. He was very, very limited, and that's why he got pushed from the baseline. As limited as he was, he tried to turn the tides via bulking up, which meant gaining weight, getting slower, becoming more prone to injuries.
Once he lost his legs, he was done as a major winner/contender.
I have never seen him display a tennis as impressive as I have seen Thiem. On the other hand, I saw him get squashed like a bug and completely annihilated. As in the 04 US Open finals.
I was a fan too, but by now, one should see how limited Lleyton was.