After discussing the issue with people who do understand how foils work (mostly with Tom Speer), the conclusion was that asymetrical foils or symetrical foils with an angle of attack actually make a boat faster.

Contrary to common belief, they do not make the boat point better - they improve speed by means of reducing drag.

A summary:
- Asymetrical or angled foils allow a boat to head lower while still obtaining the same lift (less drift).
- The boat points closer to its path over water (heads lower).
- The hull's contribution to lift is reduced and a greater % of lift is provided by the foils.
- Since the foils provide lift more efficiently than the hull, the total drag is reduced and speed improves.

Not so complicated, after all.