There's not much info I can find on how much that drag is. Plus it's all variable based on the boat towing and the conditions. But my OP on the utility of davits is, their benefit in light air sailing while allowing easiest coastal sailing(which involves going ashore for 95% of us), not daysailing, racing or cruising offshore.

Here's my opinion on dinghy damage to a sailboats light air performance, on a scale of 1 to 10;

Davits-0

Least drag is a hard dink designed to tow, some could come in around a 3 in light air.

Next are inflatables. I suspect an RIB is better but those I observe also have the tubes dragging. But a soft floor must have the most grip going through water. I'll give them an average of 6.

And dead last are all types of dinghys, towed with an outboard.

And that happens more often than people like to admit. I saw a few out in the beautiful sailing conditions that varied from 0 to maybe 12-13 kt gusts(settled, no seas).

This racer even had a reef in the main. It was sailing well to windward despite a medium sized RIB and outboard on a bar tight painter.

Look at the bone in that RIB's teeth! I give this an 11.