Maybe I'm biased since I never was a fan of the ECW garbage style, but I stand by it. I know he was doing stuff that was unheard of in 1994/5, but his legacy at this point is pretty much no showing events, missing 75% of his signature spots and throwing fits afterwards, and asking every fan who ever attended an ECW show if they have any weed. Hell one of his most famous moments was giving Chris Benoit his Crippler name by botching a backdrop. Plus he managed to be unprofessional enough to get told to GTFO by both WCW and WWF/E (twice!) despite being a relatively hot commodity at the time.
I'll be fair and state that maybe there's an amazing Sabu match somewhere that I've never seen that would prove me wrong, but it seems like he's more or less a case of Paul Heyman managing to convince everyone the Emperor was wearing a fancy suit of clothes.
Sabu was fired by WWE not WCW, he refused to sign a contract in 95 and Paul cockblocked him in 2000. Either way I don't see what that has to do with being the worst wrestler ever.