Slow down in your conclusions, ok?
And yes, you may need to read or research a little more.
Racing sails, are allways fabricated including all the triming possibilities in mind. The leech and foot lines are one more of those possibilities, because sometimes that makes a difference, and it is better to have all the possible tools than not having them.
(I have used the leechline, when cruising with my wife and small baby, only to stop the leech of the genoa from vibrating and annoying us, was is fine triming?? no... but made the ride smoother!!)
Here is an example of a well known sailmaker :
attention: Foot lines only used on Genoas, not mainsail. (but I have seen a boat with them, too!!)
The outhaul can and is used to stretch the sail to meet particular sailing conditions, such as in "stronger winds", for example, (and no crew on the rail!!) but also used to give more camber (curvature) to the sail in lighter winds, (more lift) it is a very good tool to shape the sail, and should be used together with the Boomjack, the backstay, the cunningham (also have one)and the main track car, to make sure that the wind entering the sail, does "its" work and exits the wing, sorry sail, as fast as possible to make it smooth for new wind coming in. The leech line (and I used the flap name just to explain it in an easier way, because english is not my first language!!
) is just another tool.
Note that wind velocity and angle 30' above the water are different from the ones at water level, thus the need for twist (I hope the right word) - backstay, boomjack and traveler.
On my boat, my outhaul can travel up to 30', because that is just one more tool I have should I need it.
This normaly gives you more camber along the vertical axis, but the leech line "closes" (I need help with the english here) the the trailing edge. of course common sense must be used because it can overshoot your needs, just like the traveleres, the boom jack, the backstay etc.
As far as using it on the genoa, it is doing excatly what you were saying by curved wing tips!!! It is there to camber the lower end of the sail, (horizontaly) and making sure that the wind coming thru the lower end of the sail is nor washed down verticaly but rather pushed towards the trailing edge of the sail. I don't sail with it closed at all times, but it is there should I need it.
(I often look at the foot of my son's Optimist, that is attached to the boom, and see that as a very very good example of that "horizontal" camber in the lower end of the sail. can you look at an optimist sail??)
The leech and footlines (footlines are used almost on every racing sail) are just more tools, and I like them. Sailing is a constant learning curve, and I like the "gizmos" ehehehe
The fact that I include them in my cruising sails, is just another tool to fine trim the sails. My boat was built for racing, but because we sail all year round, and do some cruising, (inside it is 100% cruiser, 3 king size cabins, 2 heads, etc.), however, even cruising, I can't stop..... tell tales, cars, cunningham, I monitor them all the time... Its my way of amusing myself on a boat (which is my objective), other people have wine and listen to Pavaroti.
Hope I helped and excuse my lack of technical words.
PS I am an Aeronautical Engineer, also, so perfectly understood your questions. Planes don't use their speed brakes all the time, but they are there!!
While you are at it look at aspect ratios and downwash!! Just a tip!!:
the photo bellow shows the Horizontal camber that the foot line can help provide. A picture is worth 1000 words.
Also note that my genoa works inside the rails. And the rail at the fron is open so we can bring it out when needed.