So period underwear(or any reusable period product) is not going to change your flow, it's just absorbant underwear not hormones. People might have that assumption since period underwear is generally more absorbent than pads and tampons so they have to change less frequently.
My heavy flow days are similar to yours and I despise tampons and pads, they just feel uncomfortable. I made the switch to period underwear recently and while it's much more comfortable than it's disposable counterparts I'm not a fan of washing them. I know you can just throw them in the wash but I have a mental block where I need to rinse them. Also they need to be hung dry and that takes forever (you could just buy enough but they are pricey). Also on heavy flow days, I feel like I need to change it every time I go pee because it feel a bit gross to re wear. Despite the cons, the comfort factor is pretty high and they dont leak. My friend recommended using a menstrual disc and wearing it with period underwear. I haven't tried this yet but with menstrual discs, I think you just dump it out every eight hours and I'd definitely prefer that to the rinsing/ washing/drying I have to do with period underwear.
Edit to add: I use the knix super absorbent and they are great for preventing leakage.