I am not doubting nor questioning what you're saying, but this doesn't mean that the iPhone doesn't have reception issues, I was just mentioning my observations regarding using my note 3, my ipad and my son's AT&T iPhone 5s at the same locations indoor and outdoor, may be T-Mobile signals at your location is not great so with the iPhone things got worse, didn't you say you have a signal booster from AT&T? when I was with AT&T I had a Nokia N8 when my whole family came to visit well about 8 persons with their iPhones and when we went to the Mall you know how the signals can be inside stores, well I was the only person able to have my N8 phone working. their iPhones were useless.
I have a friend in Canada a big fan of Apple products iPhones, iPads, MacBooks, Apple TV you name it, hey he has several devices from each item, he also have a Samsung note 2, supposedly his 5s is with a better carrier and the note is with Wind which is not a big company with less coverage, when I call him or he calls me I face more issues when I call the iPhone number, the connection is not great most of the times it doesn't matter what phone I am using, it could be my note 3, a magic jack number or whatever, I am not a fan of iPhone and I am not promoting Samsung either, again it's nothing but my observations, may be Apple uses weaker Antennas that might be more safe on our brains and bodies, but for sure it's aggravating when we feel disconnected from others