I raced longboard for many years, finishing up with an Mistral Equipe II XR, and I agree with your assessment. It's been at least 8 since I sold the Equipe and have been on Formula ever since.
Although I have never sailed a hybrid (Phantom), I doubt they could better than the old longboards in under 10 knots. The Phantom offers something for everything, but can't compete with Formula in stronger winds or old longboards in light winds.
When I had my Equipe, my largest sail was a 10.6, but it had a very limited range (no twist in the leach). In light winds (under 8-9 knots), the sailboats have the advantage to windward and leeward. In 9-12 knots, the Equipe could do better upwind, but not downwind. In 12 knots+, the Equipe could do better upwind and downwind.
The above are guesses since it has been 8 years, but when I had the board, I had fun trying to chase and pass keel boats, both up and downwind. I even joined in some races (staying out of their way) to see how I could do.
Formula 160; iSonic 111; HiFly Move 105; Tiga 263; '85 Mistral Superlight.
Maui Sails TR 11.0; 9.2; 8.4; 7.6; 6.6; Maui Sails Switch 6.0; 5.2; Maui Sails Global 4.5; 4.0.