EXACTLY.
And that is all this man is trying to say.
Before, Slade truly was the best at what he did. He wasn't overpowered, he wasn't Kabal, not even fucking close, he just happened to be the most adept at the one tactic of fighters that apparently everyone loves to hate. Now, he has - still - unjustifiably been deprived of that title and relegated to a completely different corner of the IGAU metagame. The problem isn't he isn't viable, the problem is that Dave himself is inherently a zoner at heart, and follows suit in every fighter he plays, and he's infuriated that many another character were either left untouched or dropped via DLC that are just as powerful by virtue of their tools as old DS was before, if not more so. The character that fit best into his niche of play was pretty much forced to change from the ground up and become a type of character that, while still capable and quick in different rights, can no longer hold the same high tier amidst his comrades that he did before.
He isn't tirading on his own behalf. He's doing it because many others, like myself - yes, I'm still maining Deathstroke, adapting, growing, winning, etc., but at the heart of the argument I still agree with him 100% - believe as he believes, and want to keep our fellow outright or secretive zoning brethren/masters on the same page, regardless of how many people may want to smother the argument or act as though there's no reason for anyone to be flustered. ESPECIALLY with Hanzo's arrival.