You simplify too much.
Compression increase alone offers a limited improvement in power, when you understand the balance of comression and fuel octane. A lower compression with lower octane can perform just as well, as the higher compression and octane, if the cam timing and air management are unchanged.
Low octane fuel burns fast, to the point of detonation with high compresson, if the timing is not corrected (retarded). Combine this high compression and a stock cam and chamber finish, and you risk compression ignition detonation (Diesling).
Does the high octane fuel needed to correct these problems have more BTU's (heat/power content) that the low octane? No.
You can dump the same quantity of high octane fuel with high compression, and benefit little from the effort.
What high compression can allow for is longer cam timing and more free flowing intake and exhaust systems (to pump more combustion air into the cylinders each engine revolution) without sacrificing low rpm power. This "equivalent to stock low rpm compression" is the result of higher static compression combined with a lower effective compression due to the longer duration cam timing bleeding off airflow efficiency at low rpm.
Yes, you can mill the head to raise compression, but it will not achieve much unless you change cam timing as well (and fuel delivery, intake & exhaust porting, and other power factors).
The experience of most modern era (87- present) AMC six builders is you will risk detonation and possibly lose power (after correcting timing advance) if you do not change the stock cam when raising compression. The stock 4.0L engines are well balanced for cam timing & compression (they need to be for emissions).