You're confused because the food chain doesn't end with the modem.
Cell telephone handset -
Central processor controls and routes -
Phone app with analog/digital voice converter software (vocoder);
Radio firmware for the system;
Modems, such as the Qualcomm units, famously misidentified by dumb news blogs everywhere as "radios";
Radio transceivers - never discussed, but these are the key link between the modem and the antenna;
Antennas - once just stamped metal, now they're powered devices;
Kernel software modules added or modified by the phone maker to make all of the above pieces work.
If you're unable to pick up a weak signal or transmit very far, the two things in the food chain NOT responsible are the vocoders and the modems.
Any blame lies squarely on the phone manufacturer for not getting the other parts right.
Modems, regardless of who makes them have been misidentified as radios since they appeared in the first Qualcomm Snapdragon in 2010.
In reality, they're nothing more than an important signal converter - MODulating and DEModulating (MODEM) - for digital signals.
So -
Microphone/speakers - amplifiers - vocoders - processor - modem - radio transceivers - antennas.
Vocoder - software signal converter.
Modem - hardware signal converter.
(Insofar as they're not purely one or other but more leaning heavily one way or the other.)
They're just the plumbing fixtures or the joints. They're not the power.
Qualcomm does not supply the radio transceivers or antennas.