Well they do have a god in our solar system so...

The Vex need not worry about us. They are outside of existence. They were, are, and will be. They grasp the ungraspable. In their hands lie the the ability to determine whether or not we exist. They are able to unravel time itself. But, they are curious little machinations. They wish to see where we will lead ourselves. How far we can go. They strained against the power of a God and locked themselves in a stalemate for eons. Nothing we do will scrub clean the stain the Vex have left. Because while we might erase them from our timeline, there are millions of other time lines in which we failed and the Vex still exist, which means they can be pulled into our timeline to rectify the mistakes of their predecessors. They will exist with the finality of time, meaning as long as time, matter, and energy exist, so will the Vex. They have reached the pinnacle in Sword Logic, they can be killed, have been killed, or will be killed, but never exterminated, meaning they have surpassed Death, the void. The fate in which all beings, even the Pantheon of Hive Gods fear and strain against. The Vex did this without the worms, without a traveller, and without light. They did this with cold calculated infinite simulations. If time itself can't be stopped, then the Vex will surely outlast even the last, dying star, and be left to rot in the void of their own creation, all out of curiosity. They have no fear of death, nor do they wish to exist. They just simply do. Did. Have done. But why do we fear the Hive? They are our antithesis, and yet our mirror image. The Vex are abstract, and have not shown any incredible show of force. Except to the Hive. Because the Vex could not understand the Hive. They could not process their loyalty and ferocity to their gods. And their God's ability to manipulate matter on a scale that rivaled their own. So they tested them, and the Hive passed. The Vex could not dethrone Oryx, for Oryx existed outside our demension, while simultaneously existing within it. The Anilahtor Totems constructed to keep the Vex at bay were Ontological weapons, weapons that ceased your existence. The Vex learned from this and instilled that very power in their Gorgons. But why do you fear the Hive more than the Vex? The answer, put simply, is that the Vex (for lack of a better term) feared the Hive because they could not beat them. What is wiser to fear? An enemy that you do not understand nor know how to stop, or the enemy that they themselves have no way of ending. The Hive wish to exterminate all life, to reign supreme as the only remaining species. The Vex want simply to learn, but have instilled the Sword Logic into their programing turning them not only into the most efficient computers, but merciless killing machines. They do not see us as a threat, but simply a loose thread in their fabric of reality, to be burnt off at their earliest convenience. The Hive are actively seeking us out, to extinguish our presence. We broke the Hive so we could show the Vex that we will not go quietly. We will go screaming into the void, and will take as many of the souless machines down with us. The only forseeable way we could hope to end the Vex is to ally ourselves with the Cabal, the Fallen, or even the Darkness itself.

This is a lot text so be ready. [spoiler] What if later on we run into a fallen house that is part of the cabal army. We then work with the cabal on fighting the hive again. It could possibly be Oryx siblings. After that the fallen house will then work on getting all the fallen houses together. This might cause us to help defeat those that disagree in a raid or something. We might even have to fend of the vex as well. Now with the guardians working with the fallen houses and cabal empire we fight the hive again. But thus encounter will be different than the rest. The vex must have realized that the only way to survive, is by help ing the hive. Vex machines that are similar to the one in books of sorrows. We will then find out that taox is really the speaker. Since taox encounter the traveler before we did and most likely followed it. Which is also why the darkness chase the traveler. The final encounter we will have is the raid against taox and basically the whole hive army. I feel like taox kills eris to learn more on how Oryx and his siblings got so powerful. At some point we lose the last city and forced out into the wild. We might even be forced of Earth, Venus, Mercury, and the moon. Mars was not taken because the cabal empire was present there. We go to Venus because the fallen say they have a weapon to help us take the city back. The moon will contain some hidden secrets of the darkness. Osiris will tell us that there might be a way to keep the vex from traveling back in time. This will give us time to then take back the city. The raid will require whatever number seems appropriate in year 10. This encounter is different, because we will actually see the fallen, cabal, and awoken fighting. You will see the the ships fighting in the sky. Troops will be attacking around the city. There will be a certain path we have to take in order to reach the tower. This will be due to buildings being destroyed. Then we reach taox and maybe xylar the hydra and defeat them. After that a cinematic occurs showing the new golden age. The last scene will show the memorial created for everyone that fell to the darkness.[/spoiler] [spoiler]Thanks for reading all of this text. Sorry for any grammatical errors.[/spoiler]

Because we have reason to believe oryx is involved with alqaeda

Because the Hive are the ones attacking. The worms make them anti guardians basically. Not to mention they are the only race we know of that is capable of killing a ghost and therefore killing a guardian. In addition, the Hive or at the very least Oryx are the darkness incarnate. According to the Book of Sorrows, Aurash and her sisters found the worms in the deep, which is speculated to be the darkness. Aurash and her sisters were bonded to the worms and transformed. Newly transformed, Auryx/Oryx slowly built up the hive over an unknown span of time.

What I still don't understand is why is a vex gate lord is doing in the PoE, don't they control time?

The vex are not forever. The vex fear death. The hive have destroy millions of world's. They have killed the strongest in the universe. Their power has no true understanding. The vex can not use the power of the darkness like the hive. Look at the hive. The can have the power of darkness. They are truly forever. Not even death can keep their gods down. Look at the power the have. The vex invaded a hive world. Yet they failed by the power of oryx. His sister knows of the vex.

Hive are mostly bent on actively destroying us... ...the Vex are an equation being calculated. We're just in the way of a giant formula.

A better question is since the cabal are supposedly the greatest military in the system why can't they accomplish anything on a large scale

Machines aren't good or evil, they're just cold logic. That whole mission to get No Time to Explain should have made it clear if it wasn't already

Just think about Bungie's plan for this game....10 years....they are definitely taking their time. I don't have a problem with it. I think that they should spend time on all of our enemies.

The vex came from the hive.

We have not fought warrior vex only their builders. They only attack when you interfere with the construction job. Oryx is extremely powerful in the lore but super weak in game. He has taken beings of light capable of destroying planets in one swoop.

They are nearly the opposite of the guardians, those nasty worms are the ani ghost, born from darkness, and the only race with living gods, the falen are just a race the traveler have come and gone from so theyre pissed and the cabal are just a very powerful warlord race, the hive are the only ones with actual celestial power and true opposition to the traveler