But most reputed or even just known firms/companies won't be taking you for quant based roles based on your commerce background. All of the quant analysts I have seen are from a science/engineering graduation background.

Mostly true but also disagree on this. It's not essential to go through the conventional path to become a quant, while CAs have no correlation with quants, it does provide you with an alternative base and is somewhat also considered a safety net due to it being more structural and less cyclical like other jobs in recession times and also allows to you to switch careers into any commerce related field unlike quant which caters to a very specific niche skillset and this dynamicness is important because quant is a very stressful field at the end of the day, also I've encountered many accountants who have switched into quant fields later after taking PHDs in math/econometrics, there are lot of investment bankers that make the transition as well, a very few of them ofcourse, but yea that's still possible if love you the field and have the dedication for it.

Also there's no such barrier that commerce people can't be selected or won't be selected for quant roles infact alot of quants have a core background in economics and stats, undoubtedly there are alot of software engineers and math graduates too, but so to say that commerce people are unfit/won't be selected is kinda misleading.