How do I explain this best...I am not even talking about pressing from a tactical standpoint. I am alluding to first line defense, watch most encounters between Aubameyang and defenders, he rarely makes them uncomfortable.
I don't think you know what you're talking about.
How can you talk about pressing and defending from a non tactical stndpoint? Your first line of defense can only be understood in the context of the whole defensive approach. Alexis was the best example of this: He did what you apparently constantly want your "first line of defence" to do - engage opposition players - but as he did that he went against the tactical setup of the team, thus actually creating space behind him for them to exploit nullifying himself as first line of defence and just looking like an idiot.
Apart from few instances we actually haven't seen high pressing or gegenpressing from Emery's Arsenal, but a more compact approach. So Auba's held back behaviour actually fits in with the overall defensive tactics. It could also be that Auba is instructed not to press that much but to just keep the shape tight or close off passing lanes so the second wave does the actual engaging/pressing and with Auba higher up the pitch they instantly have an outlet to release when winning the ball. There's a couple of options why Auba doesn't outright engange opposition player, but to just make a statement like "he doesn't press" or "he can't press" is outright wrong, when we in fact have seen him do it regularly at his last club - when he was instructed to by his managers.