In the boating world we say that a boat can be any colour, as long as it is white.
Dark coloured gelcoat does not do well with sun. Once it has been let go it takes alot of work to bring it back. It also needs to be done much more frequently to keep it looking good.
Looking at your current state it is not as bad as when you started. A good going over with a cleaner wax, such as 3M cleaner wax, followed by the Meguires Flagship wax again should restore to the condition of your first highly successful efforts.
I have had saltwater kept boats since 1981. A tough environment to be in. There are many great products out there these days but time & sun will always destroy them without regular attention.