The phone is the only one that needs a particularly high wattage. If sharing drops the phone speed by a third, that leaves enough spare capacity to do a watch and airpods at the same time (with both of them getting more percent per hour than the phone). That's still a pretty good experience.

What if they couldn’t get the multi coil design to work charging ANYTHING at high power.

Maybe it was capable of charging the watch and the AirPods just fine, it was the phone’s power demands that were the thing killing it.

Definitely one possibility of many! That's why it's so hard to guess which one or two aspects really tanked it.