My thinking is this for your problem.
IF it's taking THIS long to sand out something of this size,
Your paper is clogging and your NOT sanding,just rubbing,your "polished" look.
Your spraying the lacquer guide too heavy and clogging your paper with IT.
Fact is, Wet or dry,it should not take this long.
When I do dry sand,I keep my paper blown off with air.