It's worth giving the podcast I linked a listen. In fact, I just listened to it a 2nd time yesterday after posting this. And it's 4 years old already!
It sounds like the primary reason you need(ed) high pressure, in addition to assumptions about rolling resistance, was to increase air volume to protect the rim. As the tire gets wider, the air volume goes up, so the required pressure to protect the rim goes down. Which is why a narrow road tire can have a rim impact at 40psi where a mountain bike tire would not have a rim impact on the same obstacle at 40psi. So, the wider tire ALLOWS you to run lower pressure and not damage the rim with impacts -- completely leaving rolling resistance aside.
Which means you’re dropping to 75-100 PSI... which is also a big change from 120 PSI.
1.5 the width and 0.65 the pressure is a “big” change for a part like a tire.
That it’s because we assumed something untrue about the mechanics is fascinating.