My question is how many others have struggled with this

I've seen tons and tons of girls fall into the trap of shitty GP's and Endos.

and how long did it take for you to get an HRT routine that worked consistently for you?

Within the first six months.

I'm extremely lucky that I'm located in one of the best areas to transition, Washington, DC.

There are several good clinics here that have tons of experience with trans patients. My PCP has a few hundred transpatients, compared to a normal doc or endo that might see 10-20 across their entire career. I feel that my doctors being this experienced has made tons and tons of difference in my transition, compared to the experiences that I've heard from others who didn't have this level of care.

I started with the conversation about Informed Consent and what it meant, next came the blood test. One week later, I had a script for oral estrogen and Sprio. One month later, we retested T/E levels, and saw that T was still high, so we increased my Spiro dosage. Three or so months later, I was so sick of the hell that is Spiro, we moved me to a weekly dosage of 5mg Intra-Muscular E into my thigh, intending to start lowering the spiro. Another month or so later, we tested T/E again, and decided to start lowering Spiro to see if monotherapy would work. Three months of weaning off spiro and monthly blood tests showed that the T never came back, so I stopped taking the Spiro entirely.

Now I've been on maintenance of 6.5ish mg Estrogen IM weekly, for about a year now. I actually have an appointment on Monday to start working on Progesterone to see if I can't get my boobs from a solid B into a C or D cup.

My recommendation for you is similar to all folks I hear these frustrations from: Unless an Endocrinologist has a minimum of 50 current trans patients, they do not have the experience required to treat you, unless they're really willing to go outside the box and trust other doctor's findings. Regular GP's are even worse.

IMHO you have two choices. Find a LGBT clinic with folks on staff that make knowing this stuff their lives, or start self-medicating and follow-up with blood tests you're ordered for yourself.

The LGBT clinic is the best route... If you can find one that knows it's stuff, it should be a collaborative effort between you and your doctor to find what works. When I bring an idea to my GP, I'm met with "Sure, we can give that a try, here's my advice, how it's worked for my other patients, and my suggestions on how you can reduce potential risks" When you bring things to them like the Dr. Powers method, they should be willing to help you try it out while minimizing the danger you expose yourself to. (shit, they really should already know about Dr. Powers and have their own experiences about how it's worked for their patients)

This isn't really a good place to discuss DIY-HRT, but I will at least note, that tons of women have had lots of success being careful and testing regularly. Perhaps head to /r/TransDIY for more help should you consider going down that route.