I don't think his defending has ever been brilliant and he's showing that he still has that lapse in concentration that can punish you.
I agree re all his other attributes and he'll definitely improve us. However, there's no point in overrating the guy. His speed basically saves him in the majority of situations.
At the end of the day he's 1/4 of the best defence in the league by a mile. If we get him, we know his defending is good enough to not be a weakness in that Spurs defence.