Bairstow has some middling scores in the better innings and crucially, failed in the second innings of the defeats. That's still better than Buttler, who hasn't gone past 25 in five innings. Surely both can't play. Depending on who keeps wicket, the other doesn't deserve to play as a batsman only. Given their ages and their modest records, neither should be playing Tests beyond the Ashes.Drop Ali, keep Bairstow, bowl Root.
Agreed that Mo hasn't had a good series and this hasn't really paid off. Root is a very effective bowler now, but is a second spinner - if Mo is left out, Leach should come in.