I genuinely don't think I've ever played a gacha game where the main character is not only good, but actually competitive in endgame content. Harmony Trailblazer rules - they offer a unique (for now, at least) game mechanic, generally strong performance in their niche, and to cap it all off they're stylish as hell.
Starter characters in gacha games are usually just there to get you through the early game and past your first few pulls until you get better characters. This is true of Physical TB - they're a straightforward damage dealer that helps you get to grips with the combat mechanics, but they fall off hard once you get to later-game content. Preservation TB is similar: they offer a nice bit of a variety and can be used as a secondary sustain/breaker but ultimately don't compete at higher levels.
But Harmony TB? Hell, they're one of the best imaginary breakers in the game, their team damage output is impressive with Super Break, and they elevate break-focused teams to offer performance more in line with existing DoT and FUA comps. Most importantly, they serve as a freely-available substitute to Ruan Mei - who is widely agreed to be the best universal support unit in the game and is highly recommended for many team comps, but many players don't have her (anyone who started playing this year won't have had a chance to get her, for example).
So, props to Hoyo. As a Ruan Mei-less player who loves Gallagher and Xueyi, my Harmony Caelus will be seeing a lot of use. And with free Dr Ratio as well, stomping imaginary-weak fights has never been easier. Other gacha games could never.
EDIT: Just to stop the endless stream of comments about it, I'm not saying Harmony TB replaces Ruan Mei - I'm saying that they can act as a good substitute for her for players who don't have her, because they can be used to enable break teams, which nobody other than RM could do previously. Obviously their pair extremely well with RM.
Also, it sounds like I should check out Granblue Fantasy 😅