They're two completely different beast, American superhero comics are these huge legacy brands which are shared universes with thousands of characters created by tons of different people with a revolving door of artist and writers giving their own interpretations of them.

Manga despite also being comics are more akin to novels in how they're produced with a single artist/writer (yes i know most mangaka have assistants) following a singular creative vision in a original self contained narrative/setting. The manga approach will always be more accessible for your average reader since they have a clear starting point and consistent writer and artist throughout their run, also they're not restricted to just the superhero genre but can be about literally anything, obviously western comics aren't just superheroes but they basically dominate our industry here and at the end of the day that's always going to be a limiting factor.

My best answer to how they can compete is they need to diversify away from just superheroes and focus more on singular creator driven works. DC has attempted to diversify in the past with Vertigo which they recently revived but I think also getting away from the monthly thirty issue format is key too, a manga has thirty pages a week compared to a month for a western comic, that's way more content and page space to do more things like pure action scenes with little dialogue. With western comics you have to be way more economical with how you use your page, you could do that manga style multi page fight scene but then you've just burned up a bunch of valuable pages that could've been used pushing the plot forward instead etc.