Well I have to say I very much disagree.
For Sidious to pass up Talzin in favor of Maul, seems to suggest that Maul did have great potential. You also have to remember that he chose Maul long before he had any notions of Anakin even existing, and all the old canon material suggesting that he was just trained as a assassin for Sidious has been thrown out and even seems at odds with his new backstory. So he's effectively found this very small child and obviously seen something that made him want to take him on as an apprentice and eventually bestow the title of "Darth" onto him.
And then you look at his actions after his first real defeat, he was cut in half and yet he survived through sheer will and some unspeakably dark ability in the Force. That's nothing to brush off, he's effectively used the Force to cheat death and in the canon the only other person to do that was Anakin. After that he manages to fight Obi Wan on a pretty even basis, and even drive him to retreat in one instance. He's fought Mace Windu without any real difficulty and has bested and outplayed Dooku. Also, it's worth noting that when Maul had his uprising on Mandalor, it was Sidious who faced him and not Dooku or Grevious. The fact that he'd actually come out of the shadows for once and directly get involved speaks to Maul's threat.
If we were talking old canon, I'd be more inclined to agree with you, but the character has gone in a vastly different direction under Filoni and Katie Lucas.
