Bronya has anemo dmg and crit dmg traces. One passive gives 100% crit rate to her basic atk. Her E gives 66% dmg bonus at lv10 (for 1 turn), while also cleansing the ally and advancing their action. In other words, she is just a very well designed support, arguably the best of the standard banner characters.
Her Q gives atk and crit dmg that scales on her crit dmg. So one can stack crit dmg on to her.
At lv10 the Q gives 55% atk and 16% of her crit dmg + 20% to the team for 2 turns. So if she has 200% crit dmg (possible) she will give 52% crit dmg to the team (at C0), which is good.
For artifacts, one can use 4p musketeer (more atk, spd, basic atk dmg) or 4p hackerspace (increase team spd after Q).
In Genshin, the 4p hackerspace could increase atk spd. Or it could shorten cooldowns team. The whole point is to make characters attack more frequently, which can be achieved by cd decrease or atk spd.
Bronya buffs dmg bonus with skill and crit dmg and atk with burst. She falls into the special class of supports called 'universal buffers'. That is, she can be used in basically any team to buff damage. In Genshin, as of version 4.2, there are only 3 universal buffers: Bennett (atk), Mona/Focalors (dmg bonus), Morax (res shred). We merge harmony and nihility into a broader 'buffer' class. The above 3 characters can be used in almost any team and buff damage.
Sometimes Raiden (ER, burst dmg) and Nahida (EM, reaction crit) may count. And Venti (nihility) is more of a crowd control unit than buffer.
To say the least, adding a Bronya equivalent in Genshin would augment the meta. Bronya could be used in many different teams. As of version 3, it seems Genshin wants to maintain the monopoly that Bennett, Mona have and be selective about what kinds of new universal buffers it adds to the game.
In Genshin, Bronya's E could buff all dmg bonus (say give 40% dmg bonus), while dispelling a debuff on the character. It should be comparable to what 1k EM Kazuha E can do for the autumn elements. At the same time, it should be less than Mona's 60% dmg bonus via Q given it is an E skill. Bronya's Q can then buff all party members' atk and crit dmg (it can scale with Bronya's own crit dmg too) for say 8-12s. The atk buff should be less than Bennett's buff (or else Bennett is out of business). The crit dmg buff could be 30% to everything. If it is 40% or more it could powercreep other effects like Gorou c6, Kujou c6 that give elemental crit dmg buffs. The universal crit dmg buff alone would make Bronya a universal support and unique in Genshin.
If one wants, Bronya can have a passive where using her NA/CA decreases the cd of her E. Another solution would just be to give her E buff 100% uptime.
Observations: Ruan Mei's advantage is she can buff the team damage with her E and is more sp positive. Bronya E is ST but her Q buffs the team but may be more sp-neutral depending on how you play her (there is fastya/slowya). Bronya can also cleanse and advance action, whereas Ruan increases weakness break efficiency with E and res pen with Q. Overall, Bronya can probably buff a hyper a lot more as her atk, crit dmg, dmg bonus buffs are insane put together (great for JY, Blade, JL, Ratio, etc.), whereas Ruan's main advantage is being more sp friendly (so for QQ, Lunae) besides her niche of modifying weakness break.
For JY, one may argue that Tingyun or Ruan Mei can be more or as effective in some situations as their buffs last several turns and given how the LL works.