Listen to what
@MichaelNadal said. It will easily go down as one of the top 10 tournament performances of his career, including slams and everything else. The circumstances, his age etc.
Davis Cup is a unique competition and has to be judged on it's own merits, like the Ryder Cup in Golf. You play singles and doubles as Nadal did, but you only win the team title (though he was named tournament MVP for the 2019 edition). It has zero correlation with trying to pretend a doubles title in anything means the same as a singles title.