Ah ok boing boing. That makes sense.
I started with decapectal (not sure that was the right name) and no HRT - most horrific thing I've ever done. So yes, you need the HRT - but my guess is, the Estrogen is triggering your problems and bleeds.
Yes, the hysterectomy should sort out your bleeding. But you do want hrt established first so you know what you tolerate and what helps. So, if it was me, I'd test my estrogen levels now and, if you try reducing hrt again to stop the bleeds and become symptomatic, test again.
It's all data. And data your gynae won't collect. Then you'll know what level of E you need to feel good after the op. And by then, no bleeding.

I've just tried double dose POP and it has supressed me so far I felt like I'd landed back in chem meno. It's all so hard work.
I suspect you won't find an answer until your op. But, if you've been struggling this long, I really urge you to start monitoring yourself so you know what you want later.
How long is the wait?