It's either way for me. I don't mind if he is post or prime during Rebels, both help him in different ways.
Well if he's post prime you don't necessarily have to concede on inferiority to Kenobi(it's still hard to argue). But then you also have to accept limitations from his TCW self(like not being able to outperfom TCW Kenobi in saber combat).
If he is prime, you have to accept Kenobi as superior, but you also are free of Maul's TCW restrictions. For example, Rebels Maul>Dooku is genuinely arguable.