Well, we know Anakin's mastery of forms should not be as l33t as Obi, and we don't know what level of Mastery Maul has, and I don't have details on Maul's forms and training(someone fill it in?)
But The Maul's case is more of a surprise attack, as I think at that moment Qui is still more skilled than Obi.
As for Anakin, even if they are evenly matched, Anakin is in a somewhat confused state(being not fully into the darkside yet) so Obi did have an advantage.
Then again there is hardly a fight in this world where it is "fair" per se. Oh, and Luck, its part of the Force.