A 25dB NRR doesn't actually mean you subtract that from the outside noise. The recommendation is that you cut 5dB off of the NRR and apply that.
IOW, 165db - (25dB-5dB)=> 145dB exposure per shot.
That detail in the noise exposure guidelines is often missed.
OK, then I guess he was just saying the noise ratings are overstated. Has nothing to do with the logarithmic system.
But as I said, I just use the foam earplugs I get at Lowes in bulk when shooting and it seems quite adequate.