I know this is a work-around and costs money and isn't the solution you seek, but the back-button device you can get for the PS controllers (at least pS4, not sure about pS5) are actually pretty great and make weapon swapping with a controller a breeze! Dunno if i could play without it.
I did have an Astro C40 for a while and maybe I was just spoiled with it, but you’re right, those back buttons are fantastic. I might just grab the attachment. I don’t think they have them for the PS5 yet but I still can’t get my hands on one of them either lol