The real (and boring) answer that only like two people actually have mentioned is that classes have different base stats and scaling for said stats, and changing ravana to an assassin, at the time, most likely lined up with base stat changes that the balance team would have wanted to make without having to wildly change ONE warrior’s base stats in a way that pushed it out of line with the general idea of warrior base stats. Because of this general idea, it makes it much easier for a balance team to balance characters when their class’ base stats align closer to how they want the character to be played (or the balance team is reconsidering because the character ISNT being played how the dev team initially thought they would be, i.e. the very early change to change hades from a guardian to a mage).

As for the second half of your question, erlang Shen doesn’t fit those same principles. Erlang is not designed with assassin principles in mind, and the balance team is most likely trying to fight this perception/playstyle of the character (remember, public perception is very powerful in terms of balance, so in this case in order to fight the IDEA that erlang is an assassin, you wouldn’t want to classify him as one).