Which will never not seem weird to me. Slade's great in the original NTT stories, pre-Perez departure. He was a dangerous, competent badass. But I will never forget that it took him two years in-universe to figure out a way to kill a group of teenagers. And his plan required another teenager to do a big chunk of the work. Like, Dick could stand up to him and even escape him with an injured ankle, a pissed off Gar can knock him around, and Kory and Donna unleashed as a team or even individuals could probably take him out.
No way do I see him as the League level or even Batman level threat he is painted as these days. Terra was more than capable of killing him (and actually managed it in both adaptations), and she is not a League level threat. It may have been better for Deathstroke and the Titans property as a whole if The Judas Contract had been Slade's swan song, as it sort of was in-story at the time where he was past his prime.