I can understand all of that except using zinc instead of aluminum. Maybe think about the heavy metals that are getting into the water when you scrape on the zincs.
Like many cases, our first coastal boats came with zinc anodes. It was ok, as they never ventured into true fresh water but did see brackish. Then we were enlightened in 2014. Boat built in Washington, mainly ocean going vessel, all aluminum anodes by builder. Why? Lake Washington. Columbia River. Even the inland passage. In fact, Elliott Bay measures at the upper end of brackish. All the Estuaries on inland to Alaska. Closer to home, much of Chesapeake is Brackish. Potomac is fresh. Delaware goes from salt to fresh. We changed everything from that time to present to aluminum anodes. Simple and works for all. In Europe, what about the Thames and Seine and inland waters of the Netherlands?
Then the ultimate anode challenge, the Great Loop. We ran into boaters who were changing back and forth, talking about what a pain it was. We just stuck to aluminum. Now, we do not have any pods or aluminum drives that would interfere. With watermakers, we're more aware of salinity and I suspect very few people here boat only in one type water. Boatzincs has two sets of charts covering all waters. Not one situation in which Aluminum isn't acceptable. Boat life is complicated enough without worrying if you have the right anodes, if you need to change, if your anode is damaging the sea, so once again we refer to the strategy of KISS.
If you are 100% certain you only boat in salt or fresh then perhaps zinc or magnesium is your choice. Just remember when you decide to cruise elsewhere and even 100% salt, I'd still choose aluminum. Aluminum also has the benefit of outlasting both zinc and magnesium.
Our diver had a customer who insisted on zinc and was constantly having problems although claiming he only boated on the two coasts, about half the time on the Atlantic and half on the Gulf. However, it turns out he crossed back and forth through the Okeechobee several times a year and even spent a few days fishing the Okeechobee on some of the crossings. Okeechobee is fresh water. Switched to aluminum and no more problems.
And here is one for you. What boat material should never use Magnesium anodes even on fresh water? Wood.