"Stefan"
Also, commercial glider pilots must be able to drop the plane between
two lines 100' appart.

Which is not that impressing when you consider that with those huge
airbrakes, you can adjust your glidepath to anything between 50:1 to 5:1.

Airbrakes are far superior to flaps for glidepath control but I'm sure you
are exaggerating to make the point. Few gliders can achieve 50:1 and I'm
not sure about 5:1 either. But they are effective even if not huge.

But not always. I had the pleasure to do my initial training in a Schwiezer
2-22 where the difference in glide ratio with zero spoilers and full
spoilers was barely distinguishable (slight exaggeration). Side slips with
full spoilers were standard procedure. A nice training experience.

My first owned sailplane was the Finnish PIK20-b. A 70's vintage glass ship
with no spoilers. It had flaps that were infinitely adjustable between -8
and +90 degrees. Flaps can out perform spoilers in the sense that steep
descents can be achieved at slower speed. Problems include the need for
tight airspeed control to avoid balloning and float along with the fact that
flaps are effectively 'one way' devices, especially on gliders. Once you
roll in landing flaps and slow down, you really can't increase your glide
ratio by rolling them off. If you do retract the flaps to increase your
glide ratio, you generally have to increase your speed and/or let your
descent rate go up to regain some energy before the desired effect can be
achieved. With an engine, you can counteract that but in a glider all you
have is height and speed.

The PIK could be set down on a dime once the technique was learned. The
trick was to fly final with 90degs of flap and flare a foot or so off the
ground. Unless you entered the flare with a ridiculously low airspeed,
ground effect was sure to float you past any planned landing point. But
when you the desired point was reached, you simply dumped the flaps and
flared for a 2 pointer. However, the flaps were actuated with a crank that
required 2-3 full turns to dump. Imagine rubbing your tummy and patting
your head at the same time. It took a full season before I could detach the
cranking with my left hand from the smooth pulling with my right. Imagine a
bouncing ball..... But once mastered, you could land with a yard of any
intended point.