That's not a plot hole. A plot hole is a contradiction in a story line via 2 seperate events. You are just arguing capability and action. (What they can do and what they do with it). Assuming all we know is accurate about being a time traveling hive mind, you could argue they could just go back in time b4 we existed and just end everything before it happens. You can always go one step further when arguing semantics. Some times you just have to assume things happened the way they did for a reason.