My .02……
The lifter being soft is not the cause of the low oil pressure.
More likely, the low oil pressure(or whatever is causing the low pressure) is the reason for the soft lifter.
That's an interesting thought. I expected to find the lifter popped out of the bore, before I removed the intake.
I disassembled the lifter, and AFAICT there's nothing in it that shouldn't be. I still need to soak it in simple green and try blowing out any passages in the body.