I agree with everything you said about too much pressure and the damage it can cause. There is a risk of pressure blowing out seals or wearing out components faster than they otherwise would.
I disagree about what constitutes too much pressure, particularly on the version of the VE pump that came standard on the 4D55/4D56. Some obscene supply pressure like 50-60 PSI, sure, that's putting a ton of force on these cast aluminum housings and the components therein. I won't argue against that. I will argue that 10-15 PSI is not going to hurt these pumps, particularly if it is regulated to avoid any pressure spikes. I don't see how a stronger lift pump can cause these problems you discuss so long as they are supplying reasonable pressure. An unregulated pump supplying high pressure, maybe, but we're talking maybe low teens tops. Even unregulated pressure in the neighborhood of 8 PSI, like that OP was experiencing would not be a problem, and my current lift pump is a regulated pump we have set to right around 12 PSI (can confirm, they are not cheap units).
In regards to the difference between pumps were "calibrated" for a supply pump and those that were not, you reference the Ford ranger pumps as being one such pump. (Unless I misunderstand what you are saying in which case I apologize, and you may disregard what follows) I have disassembled pumps from 4D55s from both Ford and Mitsubishi applications. They are identical. In my experience I simply have not seen any major internal differences between these pumps that were equipped on vehicles with a supply pump and those without.
I feel like we are basically on the same page as far as too much pressure is not a good thing, but we seem to be in disagreement as to how much pressure is too much on these pumps. With the pressures I have run I have experienced no problem, except for possibly a seal failure, some of which can also be attributed to a 40 year old injection pump that had probably never gotten new seals since it left the factory. Not a serious risk of damaging the pump in my opinion, but rather obnoxious when you leave a puddle of diesel whenever you idle somewhere for too long.
I also agree with the need for a pressure gauge. In my opinion that goes without saying as it can tell you a lot about what's going on at any given time with your engine.