Think it's very likely a tactical tweak, similar to what Sarri did with Kanté at Chelsea, Walter with Ascacibar at Stuttgart, Thiago is often the deepest mid at Bayern with more 6-like players shifted higher. The thinking is you want your DLP deepest when winning the ball so he's the first to receive the ball and organize play, with ball-winning 6s like Kanté, Ascacibar and Torreira pushed higher up the pitch to try and win the ball higher up in an aggressive and tight press. The obvious problems are that not every DLP is a perfect mix of passing and defensive ability, so without a ballwinner behind him once he's surpassed it can create defensive issues, same goes for him being targeted by the opposition as they know play will mostly go through him. Another problem, especially at Arsenal, is that there's still no cohesive overall pressing system, so the pushed up ballwinner is not very useful as of now - there's still no pressing traps and the like so he's mostly just running around. You can go back and do it the traditional way of putting your 6 behind your 8, like e.g. Real Madrid under Zidane do with Casemiro sitting behind Kroos and Modric, but you'd ideally need a ball carrier in that three and obviously Emery prefers to have two 6s sitting so that doesn't seem to be a way for him. You can go about fixing this tactically via off ball movement, player spacing, decoy runs and positional rotation, but I honestly believe we won't see that. It's going to be more of the same.