I have lots of questions....

First of all, if the Vex can time travel, why haven't they won yet? Surely invading the past is the better plan since when the collapse occurred, any threats would have been easily dismissed. Second, if Cayde has a son, then unless Exos live differently to humans, who's Ace's mother? The only other female Exos we know of are Ada and the Stranger who, if you saw one of my comments in the Bungie forums, could also be Ada. Third, if the Drifter has control over Taken, does that make him a Taken King? Ok that one's not really important and I know he isn't since he was almost attacked by one in a cutscene, but hey, he could be. While on the topic of the Drifter, how was he even able to make a device that can open the umbral engrams if they're filled with darkness? Was it a gift from the Nine? A result of scavenging? Also, if the nine stand for this galaxy, and the Darkness is on our doorstep, then why haven't they done anything about it? And then, there's also the case of Savathun. Is she fighting the Darkness, or simply interfering to gain revenge on us for killing literally any other member of her family? Then there's Rasputin. Did the Warmind die, or has it gone into sleep mode, or has it left into a new host body? And then, the biggest question I have: If the Darkness was able to dispose of the Warmind like dust on a shelf, why aren't they making their move? They clearly have the capability of wiping us all out, so why aren't they doing so? What do they have to gain from keeping us alive? What are they planning?