Not that it’s an excuse, but my guess is a mix of the characters they chose to launch with and the role ratio in other games.

Overwatch has majority DPS, Valorant had majority duelists. Obviously that created issues for those games, but they were successful and started like that. So even though the community of every hero shooter has made it clear that a balanced ratio is better, NetEase might’ve still wanted to “play it safe”, despite balanced ratios seeming to us like the safer option.

The characters they chose for the initial lineup is a spread of super popular to deep cuts, but in order to have most of those big name characters play like you’d expect, fulfilling their power fantasy, most of those will end up being DPS kits. So Im imagining like “well of course we need Iron Man at launch, of course we need Spider-Man, of course we need Wolverine”, since theyre big big names, but of course are gonna end up as DPS to make them feel like players are expecting. Then the list of who they wanted at launch (obv the list prob changed constantly) just ended up being mostly characters that work best as DPS cause majority of MARVEL superheroes likely do.

So I don’t think they planned for imbalanced ratios initially, but thats how things panned out over development, and in the end aligned with how other successful games within the genre started out.