(1) He used to be a very different shade of black as evidenced by the photographs. So we are speculating that he does use a skin lightening cream.
(2) There are two types of creams (powerful prescription only stuff, and the off the shelf shit). So we are speculating that he used the powerful one given the dramatic results.
(3) The powerful creams usually contain hydroquinone and corticosteroids
https://www.nhs.uk/conditions/cosmetic-procedures/skin-lightening/. So we are speculating that he needed a TUE in order to use this cream or else he'd get banned lest he miraculously avoided taking a piss test all this time.
(4) As soon as you hear the word TUE you have to think of doping being the motivation. So we are speculating that he was in fact doping. Contrary to the bullshit paper you referred to, a review of multiple more papers
https://bjsm.bmj.com/content/54/1/8 shows there is evidence that it enhances performance in endurance sports (like cycling and football) as opposed to maximum output sports (like the 100m sprint), which is obviously why team sky were all on it.
So I have no idea what your problem with that speculation is. Do you think his skin whitened because middlesborough gets more sun than wolves? That would make you stupid. Do you think it whitened using off the shelf creams? That would make you gullible to snake oil salesmen. If not, then do you think he got a prescription just because he disliked his original skin colour that much? To the extent he went out of his way to get a god damned TUE for it despite being a professional footballer? Then you're really clutching at straws in my view. The obvious conclusion is the one staring you in the face. He got a TUE specifically to dope up, probably on the advice of the barca medical team, they played his race card to justify why he needed to use the cream, he duly spent night and day in the gym, turned into a physical beast, and suffered no tiredness when he went to train and play matches thanks to the effect of the corticosteroids.