You can skip it.
There are three good reasons not to:
Gelcoat is the fastest ways to get it slick and the same color as the rest of the deck.
You also don't get get bleed through from the fairing compounds.
You won't have to prime that spot an extra three times so you won't have a dark spot in the paintjob.
Roll on three coats, the first two with no wax and the last one with wax. Acetone wipe, sand flat... Prime and paint
I've spent a number of years of my life devoted to fairing epoxy
boats with epoxy
fairing compounds, so I jump at the opportunity to start and finish a job in polyester within three hours instead of three days of sanding
, puttying, waiting.
If you do use putty, use some good stuff like Adtech P77 or 3M's vinylester you'll end up with wee small blisters
. Bondo, and acrylic
glazing putties are fast but they take on water
and make wee little blisters. No such issues with Gelcoat.