Does anyone really make a pinhole for pressure?

I always do, because I use waterproof (commercial) hatches.

Without vents in the bulkheads, dropping temperatures (from warm car top to cold ocean over the deck) can actually cause reduced pressure that will suck water in past the hatch seal with some hatch cover designs.
If somebody says vent holes aren't necessary with wooden hatch covers, it says a lot about the hatch cover reliability, IMO.
If the flush-style wood hatch lids are really airtight, it can be very difficult to open them if the boat has cooled, without pressure-balancing vents.

With the usual small bulkhead vent hole, a full evening in the pool - with a lot of water in the cockpit - usually results in a few tablespoons of water in the compartments, at most. So it's not an issue at all in normal paddling, even if you do end up practicing rescues.