Poor assumption. I think wider rims usually keep tire height constant or even make it bigger. Think of a ballet dancer doing a plié. Similar concept. You’d only start reducing height once rim width exceeds tire width.

If you have “official” room for a 27, you can fit a 25c gp5k on a 21mm rim... but that’s about it. A 25c Vittoria on 23mm rims measures 30+.

I personally think the wide rim hype is mainly good for aero and MTB. I like mine but I wouldn’t recommend the wide rim/narrow tire combo to someone who doesn’t race. It’s like using ceramic bearings or a UFO chain or tubular tires for cruising. Impractical and not worth the marginal gains. But if wide rims get you stoked, then they get you stoked.