I'm thinking that Root doesn't think much of Ali as a spinner, and that he's pretty much going to play as a batsman.
Until he once and for all proves he's not consistent or tough enough to score regular test match runs, then we can get another batsman in. Shame they didn't just do it now, save all the time figuring out what is already obvious.
Picking Dawson seems odd, however he did perform well and they like his attitude, just yet to be convinced he's good enough for international cricket in either discipline. We could just accept that we don't have a good enough spinner and play a seam attack until one develops enough o be considered for test match cricket (Mason Crane needs another couple of seasons bowling hundreds of overs in county cricket before he's ready)