Keeping narrative "truths" for each character in mind, the Doctor, properly, doesn't deal in "magic", though his stories/show-history provide narrative means for him to deal with such things. Doom's magic doesn't equal an auto-win, given that context.
However, the Doctor having "prep", as such, isn't really the key to his winning: while he is good at long-term planning (as his 7th incarnation indicated, handily), his greatest strength lies in his spontaneousness -- he's better on the fly, more often than not, than when he tries to plot things out, and that's how he pulls most of his wins out of his ass.
Still, though, Doom is a beast, and his "narrative" comparison in "Whovian" terms would be his being the Master... *after* the Master, say, usurped Rassilon's power.
*****
In forum terms, this would end in a split -- both characters have "trump power" for winning: Doom's cunning and magic makes for wins, and the Doctor's cleverness backed by a god-level temporal being/"vehicle" makes for his. On a narrative level, the Doctor "wins", in terms of stopping Doom, but Doom escapes and/or returns to raise hell at another time, thus being "undefeatable", and costing the Doctor dearly in terms of attrition.
Kang, to be honest, is a non-factor in this, and is overshadowed by the two primary combatants (no offense to Kang, but this is a case where the *narrative* truth simply is too great to ignore, and overrides the Forum Rules, contextually, due to the demonstrated feats involved).