I too am troubled by your post @Temple . It would seem your medical support team has been disappointing. At the beginning of treatment I changed one of my oncologists as I did not feel comfortable - I guess I was lucky being a private patient I could choose my team.If you can maybe you should too.
Re Letrozole nobody starts hormone therapy lightly but we choose to do so as Er+ breast cancer in the hope that it prevents recurrence ie it’s the best shot we have post surgery/ chemo/radiotherapy - we are lucky in that our Triple negative sisters have no such option.
I do not defend Letrozole, it was the scariest part of my treatment for me esp given my pre existing osteoporosis but I’ve tried very hard to manage it’s side effects . I realise some find it very tough but many find it doable - I’ve been lucky to be in the latter.
Finally I think it’s important to try , garnering as much information as you can to try and find a pathway to manage side effects for the potential protective benefits.