People dont realize that these higher levels of N and P are not natural and likely could be toxic, "although they're doing ok in those levels". It's hard to argue against it when Joe Blow DOES have some pretty colors, but the growth isn't there, or Joe Blow's corals aren't actively dying (yet). However, if you've been in this long enough (as I KNOW you have been, me too), there's just not enough justification (experience) to run these "acceptable" higher levels. In fact, it's just not needed.
This thread is a prime example, I feel, of Murphy's Law. Things compounding until it gives way: high N, P, low PH, high-ish Alk... corals and systems can probably deal with one of the listed issues, but NOT ALL at one time. Also, people shying away from running lower N and P levels, simply don't know how to do it, imo. Throughput, throughput, throughput. Heavy in, heavy out, leaving what is needed in the tank. Very different than feeding little and heavy export.
You get it.