Alright I just quickly spent the past three hours trying to watch some Avengers Assemble episodes on youtube.Thanos look superior to Hulk and Thor, but so did Attuma in the episode Depth Charge until Hulk got the same glow Bruce Leroy did in the movie The Last Dragon. He then manhandled Attuma.
Attuma, as with many villains apparently never looked that good again, and was manhandled by Hulk and Thor in the episode Bring on the Bad Guys, heck one scene he runs from the Hulk.
And Attuma gets one shotted by Thor in episode 25, Exodus.
Hyperion in his first appearance looked better than the avengers in the episode titled Hyperion, where he stops the asteroid the Avengers failed to and manhandles everybody, taking Thor's cape cause he like the cut of his jig.
But when he reappears as part of Red Skull's Cabal he no longer is a team threat and instead takes on the Hulk in one on one brawls which Hyperion constantly gets the better of Hulk in episodes 25 and 26, Exodus and The Final Showdown.
But in episode 26, Hyperion gets taken down by Iron Man's Avenger Building defenses. Takes him right out in the most ridiculous manner imaginable. He gets snatched up by a robotic arm he can't break, thrown into a water tank, and frozen by some coolant gases.
So looking at how past villains fared over the course of a season I'm going to wait and see how Thanos's showings evolve over the season.
Right now he's superior to Hulk and Thor, but that can always change. I would say he's like Darkseid right now. Original Darkseid looked stronger and tougher than Superman in episodes like Apokolips Now where he killed Dan Turpin.
http://www.youtube.com/watch?v=v0pcChyV6o4
Keep in mind that even this Weak Superman (he was put down and omega blasted earlier) was capable of shaking the city of Metropolis with his punches.
In the episode Legacy Part II a pissed off Superman managed to defeat Darkseid by redirecting his own Omega Beams back into his head, with the palms of his hands, in an explosion that wrecked them both. But Superman was tougher and threw Darkseid down to his slaves.
The first time Superman looks clearly superior to Darkseid is the Justice League episode Twilight where he beats him in a back and forth fight within Brainiac's giant planetoid construct.
By the time we get to Destroyer, a Darkseid merged with Brainiac is slapping Superman all over the place and states he is stronger than he's ever been. Superman gets manhandled, until he goes into the world of cardboard speech and smashes Darkseid across the city.
So right now imo Thanos is in that early Darkseid (Hyperion, Attuma), mode looking significantly stronger than the protagonists. By the end of the season he maybe struggling to defeat one hero in a pitched battle.