Here's a much, much better idea.
Take each of those groups you want people to vote on. Come up with unique tweaks for the characters in that group. Maybe add a couple more groups, even.
These tweaks don't necessarily have to be overtly positive or negative. They could be trade-offs that dramatically affect how the character is used or the benefit they offer. For example, Bossk's leadership could be changed to add 150% Protection instead of 50%, but subtracts 50% Tenacity instead of adding it. Now your BH squad is full of tanky monstrosities that will be impossible to beat with brute force, but a debuff-heavy squad will roll over them.
Here's another, slightly simpler example: instead of gaining Taunt when his conditions are met, Baze Malbus gains 50% Turn Meter, Offense Up, Speed Up, Critical Damage Up, and Advantage (he keeps Retribution). This switches his role from a traditional taunting tank to something more like the B2 Droid that punishes you for ignoring it.
Anyway, do these for everyone. Every TW event, 2 or 3 groups get their tweaks activated. Presto, you've made TW more interesting without this goofy "Vote for how unpleasant you want this event to be! Community! Engagement!" nonsense.
EA Staff