There was no need for an introduction to know the power of Li Yao's long-range attacks at this point. There's no point in mentioning the energy cannon, as the audience didn't have a direct experience of its power, since it almost canceled out the opponent's roar cannon.
But the wounds on Tiny Diamond's body were very real. You have to understand that Tiny Diamond had been injured before on his journey, but they were mostly insignificant scrapes that couldn't even be considered light injuries.
Even the form without the armor couldn't be damaged by dragon breath; at least the dragon fire breath transformed by the Lizardmen didn't harm the opponent at all. The meteorite was strong, but it was scattered by the opponent's forceful blow.
When it came to the battle with Li Yao, the effect of Li Yao's arrows was also limited; they only managed to hit sensitive spots like the eyes, at most causing annoyance rather than serious harm.