I have a problem with your opinion, not that you shouldn't have one but that even you said we hardly know anything about the Cabal. Therefore you cannot state an assumption if you know nothing about something. The Cabal have only sent a scouting party to our system, and their empire is on its way. They have the ability to destroy moons and planets. They know probably as much as Toland about the Hive, and are still learning about the Vex. They are also aware of the Fallen (on Mars). They potentially have the single best coordinated military in the galaxy and their firepower is unmatched. They are also probably the only race to be reasoned with, a.k.a we could be allies as Guardians and Cabal. This is mostly because we have enemies in common and they have some sense of rational thought. Also, we attacked them first (first mission on mars) which was an act of war in their eyes - so all we'd need to do is call out a ceasefire and say sorry about a massive misunderstanding that lead to main leaders of their scouting party to be assassinated. Separate from this; I think the Fallen will mostly likely be wiped. I know that we have yet to see the power of House of Kings, but the rest of the houses are helpless. They would need to band together to be a true threat.