If I were to have a solver coat and cap pierce max would the pierce defense max out after equipping the first piece or would I get the benefit of having the defense of both?
Another question How much defense do 5 star trinket (ex royal jelly band) provide compared to UVs
A max defense UV is not equivalent to a piece of armor, so a max pierce UV wouldn't make up for the lack of a skolver cap or coat.
For the status/defense trinkets, I'm pretty sure that the 5* trinkets are equivalent to a High UV.