@Goku
Explain why that might be? The only times Natsu was unable to eat fire was he's dealing with his own fire and when he ran into Zancrow. He's eaten natural, artificial, magical, and living fire. He's even eaten lava, molten metal, and charcoal. He's also even eaten other things that don't pertain to his element, admittedly at the cost of sickness to himself. Tsuna only has experience with Dying Will Flames. It's a huge stretch to say that Natsu can't
Tsuna could only do that with his Hyper Intuition. Natsu can also read Tsuna's moves with his better senses and Gokudera isn't exactly a close-combat specialist. Dying Will Mode isn't being used here and Bianchi is a poison specialist, not a brawler like Natsu.
Basil isn't exactly the series' best fighter either.
Hibari's good, but Natsu is still more experienced due to facing people with dozens of years of combat experience.
I don't recall what Byakuran's experience with his alternate selves entailed, so unless you can provide examples it isn't exactly useful.
Natsu has beaten people with precog and
mind-reading before, so that isn't exactly useful. In addition, Natsu will be reading all of Tsuna's moves right back.