Most of the Zellsis hate isn't because he is shit it's because of his personality. Just like Boostio (before he started playing like shit as well). I love Zellsis as a streamer. But some people find his loud personality arrogant., because while he did win with Sen, he wasn't irreplaceable like Zekken, JohnQT or Tenz.
Take Shazam for example, he literally made Sentinels. But bitchboy fans of match fixers hate him and other people don't like him because he complains and maybe his voice is annoying. But still, I doubt most of the Sen fans even acknowledge what he did for Sen. He was Coach, IGL, Player all in one and put Sen on top but still he was slowly thrown out. One of the main reasons I hate Sen and their fans.
Discord