I’m at 223 hero souls and am ascending twice a day, each time for 8 souls plus however many primals I can find by lvl 150 or so. I often double my soul intake or more off the primals I beat at lvl 130+ Before I breached 200 souls, I found that 7 souls by lvl 120 was optimal. The 7 was less to do with trying for them and more to do with the number I could conveniently afford with the income at lvl 120.
Don’t know if such is IDEAL for sheer number of hero souls, but getting gilded heroes helps speed up things a LOT once you’re into the 200+ hero level range. I’d recommend you spend ONE play-through to reach as high as you reasonably can to pick up some gilded heroes.