Bird doo lifts Brightside unless it is removed quickly- Brightside also losses most of its gloss in 2 years.
Not quite sure what birds and sun exist near your boat.....
Pelicans?
But brightside in my world and quite a few others seem to do fine against both.
Mine doesnt care about bird crap, even if left till a rainstorm ....and it does dull a tad, not being a 2 part.... so its no mirror but has enough shine to look as good as the rest of the boat. But it will bubble if something wet is left on it for weeks on end.
Unless you are doing a total makeover with a 2 part and removing most external features.....most will agree that brightside is good enough compared to the expense and labor of the alternative.
And for me, not having a climate controlled shed, I am not going to waste my time worrying about the perfect job as it wouldnt happen anyhow or on a reasonable time table.
The types of paint you are discussing are good paints, similar what we use on the assistance towboats. They dull way more and faster than brightside (we have used both, even at the same time on different parts of the boat). But we repaint the hulls every year as they get abused and the white uppers, a little dull but clean looks goid from the end of a tow line...
The best expert job I have seen on painted teak is OC Divers boat, who epoxied and filled first..... his rails look like painted glass over steel.