When the healers don’t fuck up and you don’t start lagging, lava walking is faster and safer than clearing (unless you get nothing but yellow pillars for the entire final stretch of the dungeon, which isn’t very likely).
If everyone lava walks but you and you end up having to clear by yourself, you might very well reach the end after the chest has already been destroyed.
Technically, anything is bannable.
Here it wouldn’t lead to a ban the first time, as proving an intent to grief would be difficult (you could have dc’d, something could have come up IRL, etc…). Do it often enough or start gloating publicly about it however and you could get punished for it.
Also yes, killing video game characters does indeed count as murder. Just like how tea bagging someone in a FPS match counts as rape.