I think there should be a distinction acknowledged between what different people mean by the word "ban" in this context. Specifically, I feel like there's a difference between "Global Bans" where a character is prohibited from a whole event by a governing body, and "Local Bans" where a character is prohibited from a match by the strategic choice of a player/team.
Global Bans would be (and have been, in other games) used when one character/strategy/whatever is overly centralizing -- you either use that character, use one of the few counters to that character, or are at a significant disadvantage. Akuma in Street Fighter 2, Meta Knight in Super Smash Brothers Brawl, Stoneforge Mystic in Magic: The Gathering. These bans increase the strategic space of the game, because the centralizing factor has been removed.
Local Bans are used as _part_ of the strategic space of a game. Because these characters are banned as an active choice by a competitor, their purpose is to fight against what the other competitor wants to do. Examples include champion banning from various MOBAs, and Stage Banning in Super Smash Bros. A secondary effect of Local Bans is as a stopgap to centralizing characters, this is true. But that's not their primary purpose.
In reference to errata, my personal stance for non-digital games is that the game should be as close as it can possibly be to its print version. I would infinitely prefer to ban a character from competitive play than to errata what their powers do, and cause schisms between how the game plays "at home" vs "at a tournament". Sure, there are difference already (and will continue to be), but none of the game components lie to you currently. Errata, specifically power level errata (as opposed to "oops we goofed on templating" errata) would cause that.
(Digital games are entirely different, since you _can_ make sure everyone is playing the same game there.)