You've conflated a couple things here but you're right overall. Longer hull length increases average speed and some hulls are shaped to be longer at the waterline while heeled. Some hulls are shaped for planing, which is where you get the flat bottom combined with a sharp prow (S Bottom hulls). Planing is when a boat doesn't rely on hydrostatic lift (buoyancy or displacement) but starts using hydrodynamic lift, which is a lot like lift in airplanes, and the hull functions like a wing, lifting the boat out of the water. Planing hulls are really hybrids designed to use displacement at low speeds and hydrodynamic lift at high speeds.

In general, a shorter planing hull can outspeed a longer non-planing hull. However, planing requires higher wind speed, functions better at specific points of sail, and is not always possible in every combination of conditions. So sometimes when comparing two boats, one planing and one non-planing, the planing hull will be better in certain conditions (e.g. wind speed > 15 knots) but slower in others (e.g. wind speed < 15 knots). And this can even vary based on the point of sail, where the planing hull is advantaged on tighter reaches but falls off the closer to dead downwind you get.

Usually, a hull design only needs to be either planing or length-maximizing, not both. Planing hulls are usually ideally sailed flat and non-planing hulls are usually optimized while heeling. However, some hulls are designed for both maximizing waterline length while heeling and for planing. But more commonly a hull is designed for one or the other, because it is not easy to optimize a hull shape for both functions. The reason is that if you have enough wind to be heeling seriously in a planing boat you should be flat and planing. If you are in a non-planing, heel-optimized hull, you probably won't be able to stop yourself from heeling anyways but should probably be shifting weight to achieve the optimum heel angle for the wind and wave conditions.

However, in high performance, large yachts like the Open 60, the hull needs to be optimized for both planing and for maximizing length at the waterline while heeling. That's the genius of the design. It displaces at low wind speeds, planes at medium wind speeds, and planes/maximizes water length at medium to high wind speeds, and then just does its best to stay upright at truly high speeds.

Because it is a single or double handed yacht, the Open 60 relies on a canting keel to provide the necessary boat trim to maximize whatever state the skipper is going for. Planing is obviously the ideal, but its not possible while the skipper is sleeping on a long race. I don't know the exact range of wind speeds that the 60 can plane in, but it's not every wind speed or point of sail, so there are also conditions that dictate when planing can occur. So the naval architect who designed the particular hull tries to optimize it for a certain set of conditions. But like everything in sailing it is a trade off.

EDIT: Fun fact related to hydrostatic lift and sails. I said a planing hull is a lot like an aircraft wing. For all the Reddit science geeks, Bernoulli's principle, which describes lift and is used to explain how airplane wings work, was originally developed by Daniel Bernoulli while studying sails in the British Royal Navy while on commission from the British Crown in the 18th century. Yay science!