Instead of just saying that the Sith'ari will destroy the Sith and raise them from the dead even stronger, it should say the Sith'ari will destroy the Sith and Jedi and raise them both from the dead even stronger. Why? Well, Sidous and Bane, considered to be Sith'ari, had as big an effect on the Jedi as the Sith. Bane killed a 100 Jedi in the Seventh Battle of Ruusan, and he changed the mindset of the Jedi to being more peacekeepers. And well, Sidious destroyed the Jedi entirely and then they were raised stronger by Luke.
Edit: This is Legends.