I really hoped the story was leading up to him fully snapping at one point and the Guard actually having no choice but to fight him to stop him. Now, he would have returned to normal once they could get him better at the Tree, but forcing them to have to fight Kion to stop him from doing something horrible to them or another animal could have been a really cool story. Plus, the rest of the Guard being able to forgive him after having to go so far as a fight to get him under control and a heart-felt apology from Kion would have been great examples of their good character.
Besides all of that, Kion never actually snapping kind of makes the bite by Ushari meaningless as anything but a plot device to make the trip necessary, IMO. The main in-universe reason they went was because of the threat to Kion of potentially becoming immoral/evil (along with getting Ono healed), but the fact that he never actually bore out the reality of that threat hurts the idea; he came close in Friends to the End, but was eventually able to get himself back under control even when the tuliza no longer worked. And the Guard being so confident that Kion would never turn or change (besides Bunga) despite the venom as to sing a song about it when he was at his absolute worst takes away even more of the stakes in his situation.
I get that it is a show for very young kids where Disney might not wanted to go that far, and that turning the protagonist permanently dark is never something that was actually going to happen, but it still feels like a waste. Every time he got agitated during the journey, his behavior got worse, so I feel it was fair to expect that this was building up to a breaking point we didn't get to see and to be a bit unhappy with that.