I haven't sailed on the Dragonfly, but this applies to many cruising boats, cats in particular. Any boat sails most efficiently to weather at a particular apparent wind angle. This is built into the boat (usually called Lancasters Theorem, you can look up the explanation in any good sailing physics text). As boat speed increases, at the same apparent wind angle, the true wind angle and tacking angle widens. Your VMG changes as a result - increased by the increase in boat speed, but reduced by the increase in tacking angle. If you plot VMG vs. boat speed for a given apparent wind angle and true wind speed, there is a peak: going faster will reduce your VMG. The increase in VMG due to boat speed is linear, but the reduction due to tacking angle is very non-linear. The effect becomes much more marked as the apparent wind angle widens (a cosine function). I have countless times been told by catamaran salesmen that "the tacking angle is a little wider but you make it up with speed". It is not that simple.

Two results of this are that on a fast boat, pointing angle is at a premium, as it reduces the effects of apparent wind. Second is that this effect if much greater if the boat speed is a large fraction of wind speed, e.g. in light wind. If it is blowing 30, then the apparent wind shift is small. However if it is blowing 30, seaway begins to be the major factor.

Most cruising cats, and many cruising monohulls these days, have a lot of windage on the hull, superstructure, radar arch, cockpit enclosure, etc.; also they may have an ineffective lateral plane. This opens up the most efficient apparent wind angle.

Here is the graph of VMG vs. Boat Speed for 28 degrees apparent at 10 knots true wind. 28 degrees apparent is a pretty weatherly cruising boat. The maximum possible VMG is 5.6 knots at 11 knots boat speed and 18.3 knots apparent wind. However it only drops to 5.1 knots at 8 knots BS. Increase to 19 knots BS and your VMG is actually negative:

Here is what happens if you widen the apparent wind angle to 35 degrees, still with 10 knots true wind. Maximum possible VMG is 3.7 knots at 8 knots boat speed and 15.4 knots apparent wind. This reduces to 3.1 at 5 knots. The top of these curves are fairly flat so (outside of a racing context) a knot or two extra or less boat speed changes the VMG very little because your change in true wind angle compensates. (Ignore the aberration to the right - my trig goes singular at extreme angles).

So the ability to sail fast only improves VMG up to a point, after which it is actually detrimental. This is one of the key reasons why wing sails were essential to the A Cup cats. They are achieving apparent wind angles of around 20 degrees or less. If they were doing 28 like a normal sloop, at those speeds their VMG would be decidedly negative.