The type of task you describe above is available within the rules. It is an
AAT with one or more turn points having an assigned radius of as little as
1 mile and then a larger last turn area for task length tuning. It's there,
just not many CD's or advisors use it.
Another interesting task that has the benefit of keeping everyone on the same
course, yet allowing the slower guys to come home while the fast guys go far,
is the "long MAT". Properly done, this is set too long to complete by anybody
so all say on the same course, yet, the slower(or lower performance gliders)
still get to drop off and finish.
FWIW - In my view, the many variables in contest soaring are part of what
make the sport interesting to many of us. Interesting that some folks seem to
get lucky a lot in dealing with those variables. Frustrating to the rest of
us.
UH

Gotta chime in to register my support for the long MAT. A skillfully
called long MAT is as close to ideal as I can imagine for Sports Class.
All youse CD types out the Call more long MATS!

On luck: Luck is surely an issue in any glider race. Notice, though,
that the pilots who used to win Assigned Tasks back in the days of
cameras, paper charts, and whiz wheels, are still distressingly
consistent winners here in the age of the digital AAT.