IV - Couldn't agree more.
It's a handy tool, but just like all tools, one needs to understand how to use it and how to interpret the results.
It WILL tell you the ability of the cylinder to build pressure, however if the numbers are low, it won't tell you why.

Did his oil consumption go down because the rings are working better from the additives or maybe it just swelled the valve stem seals?
If he knew before and after compression readings it may shed some light, but that isn't the case.

He hasn't told us if his ignition timing is correct or if he is getting proper advance or even how old the spark plugs are?
Is static timing steady?
We have no idea what the engine temperature is (if low, maybe he is constantly over-fueling and washing out the oil in the cylinders, thereby reducing compression)
Is the fuel system compromised and unable to supply sufficient fuel under load?

My van suffered from lack of power under load.
While I had no chain noise the timing mark tended to dance around, so I replaced the chain and gears.
Lots of problems disappeared, especially the lack of power.

So, too many variables and not enough info.
This just brings us back to the need for a proper, methodical diagnosis.
BB