I don't recall anyone ever claiming that it was truly comparable in fidelity to FM. In addition to bandwidth limitations, AM is still subject to way more interference than FM.

Maybe in a perfect lab setting it could approach FM, but... yeah. ¯\_(ツ)_/¯

An AM channel can pass 12-13khz of audio an FM channel about 19khz, they sound dramatically different though because of different equalization curves. AM stereo sounds nearly as good as FM, while also feeling "richer".

It sounds like the marketing for AM Stereo focused on the wrong things.

Really they should have stressed the range (so more station choice in more places) and the jump in fidelity rather than the stereo bit.

Convenience over quality worked for VHS vs Betamax. It could have worked for AM Stereo too.

Kinda, as I pointed out on a parallel thread, it failed for a variety of reasons.

First thing is the early AM Stereo radios didnt sound very good, mostly because of the narrow IF (a heavy rolloff over 8khz), but there were other inherent issues with AM that it didnt attempt to immediately solve too, like poor quality noise blankers.

Later on they intrigued the AMAX AM Stereo Radios did solve a bunch of quality issues with AM -

1) Wider IF (meaning more fidelity)

2) Much improved noise suppression

3) Other improvements improving platform stability (meaning preventing stereo center from shifting left-right.

If failed because:

1) poor noise rejection of AM and naturally high noise on the AM band

2) changing programming on AM (aka the rise of talk radio)

3) delay in the FCC picking a single AM Stereo standard, they decided to "let the market chose" which means for like 6 years there were multiple mutually incompatible AM Stereo standards on the air, which reduced incentives by receiver manufacturers to introduce support.