The Carrolls wrote:

What makes a sail boat overpowered?

Having too much sail area for it's righting moment.

how much sail is too much per foot of
length?

That's not a good way of determining the need for power from the sails. LOA
or LWL do not really determine the capacity or the stability of a given boat.
Length is linear, the overall size is cubic.

For example, imagine two 30' sailboats. One is a heavily ballasted full keel
boat with a 3.5/1 Beam to Length ratio and relatively firm bilges. It could
carry several hundred square feet of sail in normal weather. The other is a
voyager canoe... L/B is about 6:1 no ballast, lightly enough built that a
tall mast & tight rigging is going to distort the hull. It will only need a
hundred square feet of sail to go as fast as the other boat, possibly less.

Usually the relative horsepower of sailboats is indicated by the Sail
Area/Displacement ratio but that can still be somewhat misleadng.

How about wings in the future of sailing?

Wings are awesome but they have some disadvantages. It's hard to trim them
because you can't see the lee side telltale, it's complex to make them twist,
they are heavy and bulky to stow, they can't be reefed, etc etc.

Back in 1987 Dennis Connor did not believe that a wing sail would be faster
than a soft sail on his 60' America's Cup cat. They built the two cats and
one had a Rutan designed hook-top wing that was designed to allow limited &
controllable twist, and also have a spinnaker set from it for off the wind.
The wing sail cat was about 15% faster IIRC even though it's surface area was
smaller than the sail area of the soft sail cat.

Fresh Breezes- Doug King