We already know there are two versions of the iPhone; the one with the Qualcomm modem (which is the Verizon, Sprint, and Unlocked model) and the Intel modem (most phones sold locked to T-Mobile or AT&T). Since he is on Verizon, he has to have the Qualcomm modem (since the Intel doesn't support CDMA).
I have wondered if part of the issue is Apple trying to limit the Qualcomm modem, that the "fix" causes issues with the model that cause some of the flakiness that has been observed.
One last note: bars on different phones should not be compared, as various phones use different strength levels per bar. As an example, my car's Bluetooth shows the battery level of my phones with 5 bars. With my iPhone 7, between 80-100 is 5 bars and it doesn't show 0 bars until the phone's battery is almost completely spent. With a Nexus, 100% is 5 bars, 99-80 is 4 bars, and anything lower than about 20% shows no bars. Manufacturers do similar types of things with signal strength -- with some max bars is an extremely strong connection, whereas others keep 5 bars even after the connection weakens a bit. You need to go into Field Test mode and find the actual, numerical, signal strength to really be able to compare between different phones.