I learnt that having different iphone abo provider and eSIM provider won't work (eSIM get's deleted moment you remove given eSIM provider number from the iPhone ).
Not sure if that is just me or Swiss networks thing or general Apple .

bottom line - only way I was able to to setup Watch with different eSIM provider is using ... Family Mode .

Sounds Apple is pushing for "you must have iphone and watch" while "just watch" is for kids only

Never been apple fan ...