Green Xenon wrote:
"So I ask what would be the disadvantage of using AM instead of FM for
this?"

Short answer is: losing insensitivity to carrier level when recovering
the modulation.

Advantage of AM is reduced bandwidth and simpler demodulation.

Advantage of FM is that once a certain minimum carrier level is applied
to the detector.
the demodulated signal is independent of the carrier level. A balanced
detector allows non-linear RF amplification, insensitivity to amplitude
variations, and no response to noise which is amplitude (AM) in nature.

Disadvantage of FM is that it requires about twice the bandwidth of FM.

Best regards, Richard Harrison, KB5WZI