You cannot win this unless you can stand in the store with some other device that measures the quality of the network signal. If you can establish that the iPhone is not utilizing the signal properly then you can make your point.
Have you tried using a completely different phone measuring the signal on each?
This whole thing is a no win situation until someone can step up with hard facts to shove in Apple's face. Genius is only an adjective and not a measure of technical competence.
It's definitely impossible to win at the Genius bar.
Going into this appointment I had proof that I raised a case soon after buying my phone. Proof that the first genius recognized I had an issue but advised me to hold off until a potential software update. I also had proof of working with Apple support in sending logs and sysdiagnose files from not only my phone, but comparisons with my iPad (Air 2) and my wife's iPhone 6s. I had screenshots showing issues with connectivity taken from the same location at home. ALL of this is in my case. Even the Apple support rep told me she would put in a note to have the genius swap my phone just to try, although we both acknowledged that we didn't think it would fix the issue.
Unfortunately in this position, there's little I can do when the genius acts dismissive and runs through a set of cycled responses and actions. Yes I tried airplane mode. Yes I tried resetting my network settings. Yes I tried restoring as new. Yes I have called AT&T, even WITH Apple support on the line with me.
No I didn't go into the appointment with another device with me. I'm no technical expert, maybe just a slightly more informed consumer. I work a full time job that happens to be in close proximity to the Apple store. I'm just stating this as people make a case that I could have, should have done this/that. I'm just saying this to show I am a regular guy who didn't have hours of time at the Apple store. I did what I thought was all I could, and again it doesn't help when the genius doesn't seem willing to help or acknowledge anything (if they are even allowed to).
Again this is in NO WAY me going into conspiracy theories. The guy is doing his job. He is supposed to act like any issue is a non issue and cycle through the standard trouble shooting. Even IF he knew there was a problem, what would a genius do? Tell me there's an unknown defect and that I am SOL? Instead what he did do was VERY begrudgingly replace my phone and tell me to take it up with AT&T. And to be fair, best case what could he have done? Brought out endless replacements until maybe I got a working unit? Who knows if that would even be possible given we still don't know what the root cause of the problem is?
I don't mean to be so dour, but I am feeling more and more defeated after this whole thing. Also to preempt those who would say "stop crying! return it! get a new phone!". I understand that. I want to keep the phone, I like the iOS ecosystem etc. I'm supposed to be contacted by a senior advisor again, and then ultimately I'll have to figure out what to do. Also people saying that the same few of us are posting non-stop to complain, that's not my intention. I am just trying to update folks interested with all the details with MY OWN experience to help the conversation. I have been and will continue to be civil. Not looking for any forum drama.