It is indicative of more challenging situations where it can be a problem hearing people speaking because of background noise. For many, being heard clearly on the phone or hearing people on the phone without background noise is critically important.
Having the general ability to hear and be heard clearly on the phone is indeed critically important. Expecting it to be possible at all times and with zero background noise isn't, and nobody expects this from his/her phone. Nor am I sure what your Starbucks example is indicative of. All it tells us is that iPhone 7 has worse noise cancellation than iPhone 5s, not that iPhone 5s cancels all noise at all times. The existence of "challenging situations where it can be a problem hearing people speaking because of background noise" exists for both phones. Even if the threshold is lower for the iPhone 7, it is unclear how this difference is "critically important".
The iPhone 7(+) has better noise cancellation that the 5S, not the other way around. As noted in the original post, a 4th microphone was added to the 6S to assist with noise cancellation. There may have been improvements in the 7(+) over the 6S, but nobody has done the review to tell us, which is my point.
For some people being heard when there is background noise is not so important. For most, it is critically important for critically important calls which happen from time to time.
Sorry about the 7 - 5S confusion. However you still haven't provided any arguments for why the difference in noise cancellation between 5S and 7 is "critically important". The scenario where it is "critically important" is so contrived that we might as well call everything "critically important", including the color of the iPhone. It's ok to say that noise cancellation is a nice feature to have, but calling it "critically important" is a huge exaggeration.