The problem with the release of more heroes for Overwatch as opposed to Marvel Rivals is that for Marvel you have literally hundreds of established characters from Marvel lore and they each have their own established fanbase, even if it's very niche someone will be happy that their favorite character from comics is coming.
For Overwatch, all the characters are "original" creations and as such, they need to grow a fanbase by being interesting and/or having an inspiring backstory and/or design. Which works with most of the original roster I think, but then you begin to have redundant characters since they feel obligated to have almost every character be an amputee with bionic limbs and on the LGBTWTSFBSSPST spectrum, it's just tiresome.
I'm mostly talking about the story issues of having so many characters and a lot of them being completely one-dimensional virtue-signaling token minority stand-ins. I understand the need to have more and more characters to allow for more diverse gameplay, though I feel a lot of them are quite redundant with only minimal variations in gameplay that could have been solved by giving a tighter roster of characters (such as the original roster) a spec system akin to WoW talents, instead of adding more characters like "Oh this one is like Roadhog but his hook HEALS instead of hurting!"
Luckily for me atleast.. nobody I know personally who plays or have played cares about the story beats and put more on interesting gameplay offered in a shooter that is moba esq(pool of heroes with unique skillsets). While i'm sure there is a world where that specifically works in regards to a tighter roster; the game would have died due to fleeting interests since there is no sort of identity in a game based on the variety of heroes; but thats not say it couldn't have worked but tacking on more to a standing identity would have not been good design for something like this imo.
The idea of seeing roadhog and knowing what he does is pretty important to these kinds of games. They have already been notoriously terrible at balancing, it would have been worse if it went that route.. atleast with adding new heroes, they'll be days that quarter to half the roster is mid to low tier but you'll always have options ontop of people who soar or flunk on offmeta heroes. League is a decent example, i'm sure DoTA too..of its 100 something roster, only a quarter of them see above a certain percentage of play until either they release something that facilitates a synergy, rebalance, or new mechanic/item is discovered. More heroes is just another way of playing the same game in fresh new ways in predesigned rules.. which is where Rivals does really well in.
I'd say for a decent chunk of people, it's nothing to do with the player and their connection to the character via story.. but is how they play fun, are they strong, and/or do they look cool doing it. It runs into the sorta Valorant problem, where while maybe not as tight as you're describing.. the roster functionally works samesame.. and the only thing that are left are soyboys and girls playing it.. skill expression dissapeared, and player identity went with it.. it's too inbetween. In Rival's my experience has been that people are excited because of a long standing history but I know a few people that their favorite comic book character is x, but are absolutely playing something way different because of the mechanics of the character is more enjoyable.. for instance, my friend is a huge spawn fan.. and loves the fact Valkyre is in; but wouldn't touch that character with a tenfoot pole.. same with another friend who is a Cap fan through and through, hates the character in the game lol.. Deadpool aswell.
I do know someone who quit when Tracer is gay moment, but other than that the only people I know who cared about anything story were woman who played.. most of the guys I knew.. probably all the guys I know wrote it as a oh hey cool but does he kill? or does the thing
But I guess ultimately I can only speak for myself, I think the Cat looks fun to play.. Play's like Ivy from Deadlock w/o a damage build though ;c.. Soldier 69 looks fun as hell.. a sorta 76/Soulja crossbreed, and Kung Lao all look fun to play. And the fact they still haven't released a PvE mode while Rivals PvE mode recieved praise and the whole pivot to "2" was a PvE mode is criminal but /shrug
I think the only "story" I care about is the regional identity.. always thought that was cool. Was one of my favorite things about fighting games.. but the fact they didn't make Lifeweaver a kathoey was a missed opportunity.