He hasn't actually played regularly as a RB since 2014! Lost his place to Iorfa in December of that year, didn't really get it back with any regularity for the rest of Ken's reign, then started playing LB (badly) from December 2015 which is where nearly all his football was until Nuno came in.
The thinking behind this formation is as bonkers as when Dave Jones played 4-4-2 with no left winger with us for a while. There's no way you can have the required cover in behind Doherty, but he's still pushed miles up the pitch as if he's a RWB, and we know he loses the ball way too easily way too often, AND doesn't have the natural engine to get back over a huge distance if he's caught upfield and the opposition break. The tactics aren't his fault, in fact it actually isn't his fault that he's a rubbish RB, much as it's not my fault that I can't play guitar like Johnny Marr. But you wouldn't have me performing Smiths tracks in front of a massive paying audience.
Spurs have been a club that have finished in the top six in each of the last 10 seasons, I think. He won't get a huge amount of patience there, and Mourinho has form for hanging players out to dry if things go south.