I said comparable. And sure, why not? Sidious picked Maul under the premise that he was strong enough to succeed him.
Maul was very powerful and capable as of TPM, and remember that a big chunk of his training was outsourced to the Orsis academy and things like that. But even in his early 20s he was already comparable to people like Mace or Dooku.
Then he got bisected, which, given what we know of Anakin, should lessen his potential tremendously. Then he spent a decade as a madman, with no training or use of the Force whatsoever.
After Talzin heals him he is enough of a threat that both Yoda and Dooku sense him through the Force and are greatly concerned. And in a short while he becomes powerful enough that Sidious steps up and nips the threat in the bud.
Can you honestly say that if Maul hadn't lost half his body and had the benefit of a full 30-40 year apprenticeship, that he wouldn't have surpassed Sidious?
Even if we go by Lucas' now irrelevant "full potential Anakin is twice as strong as the emperor" quote, that would still make a full potential Maul comparable, assuming he caps at 120-140% of Sidious' power.
But leaving all that aside, in case you haven't noticed the Chosen One's potential doesn't mean much these days, with the rise of Rey and Kylo Ren.
Both experienced an insane rise in power way faster than Anakin did. Of course, Luke already did the same, so that's nothing new.
The Chosen One has lost his luster a long time ago.