I'm not sure that interpretation is correct.
Anakin was different in the sense that his potential was far, far greater than any other being's. Maul and Dooku were, much like Yoda, Mace, Kenobi and Sidious himself, just "regular" force users, potential-wise. While there are some that are stronger than others, everyone is in the same ballpark(again, potential-wise). Anakin was "superhuman", he was the Chosen One.
But after Mustafar, with more than half of his potential lost, he became just another Force user. Strong, yes, but the god-like power of the fully realized Chosen One that Sidious was licking his chops over was gone.
As for Sidious' apprentices surpassing him, I think the only one who didn't have it in him was Dooku. After 5-6 decades of being a Jedi and 13 more years of Sith apprenticeship, he still wasn't close to Sidious in power. I think he just wasn't capable of it.
Vader, even in his weakened state, was. The only thing that stopped him was that he was never able to kill the last sliver of goodness in himself. He was guilty, hated himself and never fully embraced the Dark side. His barriers were mental.
As for Maul, I think he is even more prodigious and talented than Anakin himself, though he lacks his god-like potential.
In his early 20s Maul was already more powerful than all but the strongest of Jedi - Yoda and Mace and probably Dooku. And even after losing half of his body/potential and being out of commission for 12+ years, he manages to become very powerful, extremely fast. Only days after being 'resurrected' he can already fight the likes of Obi-Wan and Ventress and gain the upper hand. A few months later he rivals Dooku in power, can fight Mace and Aalya Secura at the same time without being overwhelmed, and can even hang with Sidious for a short while.
If that's not impressive, I don't know what is. I have no doubt that if Maul didn't lose half of his body and was allowed to mature, he would surpass Sidious in power.