No, actually, you can have a 50% winrate and be trolling. Trolling doesn't refer to just intentionally feeding. In fact, the report should be switched to Trolling because the punishments are dealt even when it's not technically inting.
What you're doing is a very specific issue--- people going/getting Support and picking a champion that doesn't do one of the three things Supports do:
- Heavy CC and tank/Locket
- Shielding and Healing
- Artillery, AoE magic damage
Which either leaves your team without one of those necessary components, or forces the jungler to pick Ivern.
But more broadly, what you're doing breaks rule #4 "Have fun, but not at the expense of others." Picking a champion for the one most clearly defined role that doesn't fit that role, and thus forcing your whole team to pick and play around your sole choice goes against that rule.
For evidence, check out these two threads. Both Diamond +, and the Nunu was in fact the #1 Nunu in NA at the time. Your performance doesn't matter, because intentionally feeding isn't the rule you're breaking.
https://boards.na.leagueoflegends.com/en/c/player-behavior-moderation/FrILlWp7-14-day-ban-because-playing-nunu-support-with-smite-is-stealing-other-peoples-roles
https://boards.na.leagueoflegends.com/en/c/player-behavior-moderation/79aGu3wR-support-singed-isnt-banable-but-thats-not-the-point