Thinking about this more, I'm annoyed that Arteta had a week to plan for this game and sent his team out knowing Brighton's system, the way they press and set up, and yet decided to stick stubbornly to the 4-2-3-1, minus Xhaka and with Tierney told to bomb on in his usual fashion. Brighton had the advantage from the off because they had three players in there, whilst our midfield was basically Partey on his own with Lokonga playing left back (and playing it badly).
On top of that, the conditions were awful and were always going to suit Brighton with their direct football, but he didn't react to their dominant first half. We carried on with the same game-plan, not altering the positioning of the midfielders - bringing Ødegaard back deeper or moving Lokonga more central and telling Tierney to sit in. Very disappointing. I also think Pépé, with the conditions as they were, suiting fast direct football over our more precise and measured approach, should have come on much earlier. He offers the chaos factor that can work on a day like that.
Hopefully it's a learning experience for Arteta, he's got to get better in-game, and he has to be more flexible with the Tierney/Xhaka (and now Lokonga tactic) he is employing. This what not the right game to try Lokonga in that role.