This advice about bottom coating has no relevance the the reasons cored hulls get wet. ..
Can you explain that better?
From the article you have posted:
"How About Cored Hull Sides?
No problem. Hull sides are not submerged and are far less likely to become water saturated."
It seems to me that if you coat the bottom with epoxy you have an impermeable water barrier and the water cannot go to the core.
Regarding what is called "hydraulic erosion", well, the article is about motorboats and I don't know much about motorboats. Probably with fast motorboats the continuous pounding can have an effect that you just don't find in sailboats.
As I have said, there are sail racing boats that have circumnavigated several times, boats that have endured huge seas and were pushed to the limit and they are in such good conditions that it was made a race just to take advantage of them. I mean inexpensive seaworthy and sound boats that are still fast but not a match for recent boats. The race is on at this time, it is the Velux five oceans and the boats are:
Operon Racing (19 years old): 6 racing circumnavigations (not counting the transats)
Active House (11 years old): 4 racing circumnavigations
Five Oceans of Smiles (18 years old) : 3 racing circumnavigations
Le Pinguin (12 years old) : 3 racing circumnavigations
Spartan (13 years old) : 3 racing circumnavigations
These boats that had many names and raced an incredible number of ocean races have been subjected to more stress more wave impact (more hydraulic erosion) that any normal sailing boat during all its life time and they are doing just fine, still racing.
If that article was right in what regards sailboats, these ones would be just dust