I would say that those two examples generally toe the line of toxicity, albeit they're not particularly toxic in and of themselves. They're insulting to a modest degree (claiming the enemy team as being easily beaten), but I don't think they'd qualify as banter.
The best way to think about banter is to make light of something, without being insulting. My best example would be saying "Man, I sure got popular fast" when a large amount of the enemy team moves to gank you or expends a lot of their longer cooldowns to take you out.
But, that's just one example. There's a lot of ways to engage in banter, and even more ways for it to go over the line and become toxicity, but for lack of any better explanation, it's definitely best to refer to the definition of banter.
Banter
noun
- the playful and friendly exchange of teasing remarks
verb
- talk or exchange remarks in a good-humored teasing way.
Always check to see if your jokes and jibes fit those four keywords; playful, friendly, good-humored, & teasing. Doesn't have to fit all of them, but obviously the more the better.