Most of last year/season is a long time ago in football. I was talking about this season. And if he can't physically cover it doesn't matter where he's positioned. TBH I don't usually think he's positioned all that well, I prefer what he's done in recent games to earlier in the season but again I've not seen a lot of fullback cover.
I don't blame Arteta for any of that though, he's not a natural DM and his well past his physical peak. He shouldn't be expected to preform the role he does.