Maul's survival is handwaved. His hate kept him alive, and bunk like that. When Savage finds him, he's a crazed, gibbering, gaunt, shell of himself, with a robotic spider lower body and little explanation of how that happened and how he ended up there so far from Naboo.
Honestly, with the exception of the Mortis Arc, most of what I can't stand in Clone Wars comes from George and/or Katie. Ventress? Originally a Sith aspirant from Ratatak. The Nightsisters of Dathomir? Rancor-riding barbarian amazons. Maul? A Zabrak orphan raised by Palpatine to be as his name implies -- a blunt instrument, and his red-and-black coloring was head-to-toe tattooing he did as part of his being raised Sith, and an homage to the red skin of the original Sith species.
But now? All female Dark-side-users are either Dathomiri Nightsisters or exiled Dathomiri Nightsisters (the Witch of Endor). Ventress and Maul both came from there. The Nightsisters are unconvincing Bela Lugosi knockoffs and no rancors are in sight. Maul's markings are just something all of the Nightsisters and Nightbrothers do, has nothing to do with the Sith, and come in a variety of base colors for the 'Brothers. Also, Ventress' tattoos changed (for the worse) and she acquired human-style eyes, rather than her all-white sclera that was neither mistake nor artistic license.
That's not even getting into how George as revised, rerevised, and rererevised Boba, Jango, and Mandalorians in general. It just baffles me what he sees and likes... and what he doesn't... from the old EU. Loved Tim Zahn's name for the old Republic capitol before it became Imperial Center, so in TPM we got Coruscant. IMO, that beats the heck out of "Had Abaddon". Why not just call it Evil McEvil-Land?

He loved the "what-if" story of a Maul who had somehow survived, showing up on Tatooine with digitigrade robot legs and having a final showdown with Obi-Wan, and insisted it get put into Clone Wars. But all of his own material about Boba and Jango? Rewritten and ultimately jettisoned. All of the lore-building and world-building of Mandalorians spanning ten thousand years in the EU? We only have what Filoni was able to sneak in around the edges, where it didn't directly contradict the Will of George. The EU Mandalore suuuuuuure looks a lot like Mandalore's "moon" Concordia. Concord Dawn is still in, Jango coming from there is now back in. Mandalorians who weren't Death Watch still wearing the armor is still in, thanks to Fenn Rau (who is really supposed to be Fenn Shysa, but his surname is... problematic... outside of the US), who was also on/from Concord Dawn.
I have wished for many years that George would have recognized he was great at ideas, but hated writing, and hired an actual writer or writers he trusted to take his ideas and turn them into good
stories. Most of the implausibility, most of the fishbowl effect, most of the sheer stupid levels of coincidence is traceable -- with neon arrows -- to George. Maul is just one that has had a lingering impact, with Dave trying to take something that should never have been in the actual canon and make it even slightly not-stupid.