I think modern-day engines will keep a consistent oil pressure. My Tundra's gauge has never moved from slightly below the half way mark in 100K miles.
I just don't think the engineering on these old AMC engines was quite as sophisticated as what we have now.
Back in the 1990's, Ford realized that they were getting warranty claims from customers for things like low oil pressure or engines running hot not because the pressures or temps actually were off, but because owners didn't understand that gage readings would change based on ambient conditions, load, etc. So, they left the gages in there and hooked them up to the same on/off sensors used with idiot lights, making them in effect an idiot light with a needle. The needle always goes to the same place once the engine is warm. Warranty claims went away, sensors were cheaper, and just about the entire industry copied the idea. Including Toyota. That's why your Tundra "gage" doesn't move.
Oil pressure on ALL engines will vary as a function of both RPM and oil temperature. Its simple physics. There's nothing us automotive engineers can do about it, no matter how much money we spend on the design! Synthetic lubes will narrow the hot/cold variation, heavier weights will increase both pressures, wider spread in weights will narrow the variation again.