I don't have my boat scrubbed every month or two.
Many boat owners don't have their bottoms cleaned every month or two, and they don't get 6 years from their paint. The reason is that the products are simply not designed to provide anti fouling for that long. After two or three years, enough biocide has been released that the paint becomes essentially ineffective. This is true whether the boat has been cleaned twice during that period, or eighteen times or not at all.
The paint is 65% copper and it's a hard anti-fouling. How is this inferior to Trinidad SR?
In my experience, Ultra just doesn't perform as well or as long as Trinidad and I speak as a guy who is in the water every day, cleaning both of those products. They may have similar copper content, but after six or nine months, I can tell one from another quite easily, based strictly on how well each respective paint is doing its job.
The bottom paint does release when wiped lightly so it refreshes on the surface when the bottom is cleaned.
A boat in the Bay Area that is being cleaned only twice a year is not being "wiped lightly", especially not when the bottom paint is six years old. But if this maintenance regimen works for you and you are happy with the performance of the boat between hull cleanings- hey, that's great.