I would not call head to head more valid. I would call it higher quality. Im assuming you are referring to assigned tasks vs. timed, pilot option tasks so common in the USA (TAT, MAT).

First, 95% of the time I fly at a US contest, I cannot see or detect another glider. I have excellent vision. So, I am isolated, a ton, already. I hear that this "US contest isolation" causes a big shock to our pilots at the WGC.

Back to your question on head to head vs. pilot option..

Becuase it is harder to find a lift advantage over your competitors within a more tightly defined race format. There are fewer variables, although still more than enough line choice for the best pilots to gain the advantage. And because there are less variable, small advantages are more valuable than in pilot option, timed competition. When competitors are allowed to roam the sky, 60 miles away from your competitor while being in the same "turn area" (a typical US TAT with a 30-mile radius turn area, (65% of US tasks are TAT) ) and then "find better lift" than your distant "competitor" that is often more chance than skill. Few pilots (even meteorologists or even supercomputers) can consistently and accurately predict exactly where the soaring weather will be best 30-60 minutes/miles ahead in the next "turn area" vs. other pilots of their same level. Hell, I would argue even 10 minutes ahead! This highly variable "line choice" (even the choice of line over the next few clouds) is much more critical in an assigned task because each pilot must always ultimately consolidate his/her routing back to a common point (turn point) at the end each leg of the race track (aka assigned turn point).

In a TAT, the pilot can wander along in their new reality, often flying in an entirely different airmass than their competitors. This often decides the winner in a TAT. The concept of an actual race track (assigned task) is dramatically different than just "following the pretty clouds" as they develop in front of you (easy) and being able to choose both dramatically different lines (guesses) and also exactly where YOU want to turn (different turn locations for every competitor) in each of several turn points which make up the "competition" (TAT). Therefore, TAT (or MAT) tasks are simply not very high-quality competition formats when compared to assigned tasks as the number of variables are infinitely higher. And therefore chance is a much greater factor. This is why FAI (rest of the world) only chooses TAT in poor weather when giving the pilots options is sensible and the intentianal loss in competition value and quality is justified.

Assigned tasks are also not defined by a minimum time, which is always a huge decision (aided by expensive hardware and software for many), in the MAT or TAT. A huge amount of points are gained and lost in that "where to make that final turn" TAT guess (or more accurately your fancy computer calculating this for you). In a MAT, large portions of the task is "pilot option" and therefore chance abounds in each of many "guesses." Chance is enormous in these "pilot option" task types. In an assigned task, the competition (FAI, not the USA) is at least a race around a set racing track. The objective is simply to go as fast as you can, period. Less variables. Less chance. Higher quality competition.

Head to head sailplane racing only truly exists in SGP. SGP is fascinating to watch. It is simply not the leeching, gaggle fest that some would claim. It is actually quite the opposite. The field thins out amazingly quickly. SGP is extremely high-quality competition. Every decision is critical..

In all other forms of current soaring competition, even the WGC, there is absolutely zero limitation on pilots choosing their start time (a huge, HUGE variable...too huge). You can wait until 4pm or go as the gate opens at 1pm. Now add a MAT task to that competition format which already allows such starting freedom (chance). Or even add a long MAT with 30 minutes to burn on pilot choice turn points at the end of the assigned turns. Or even a wide radius TAT (22 miles is average in the USA). These pilot option tasks are highly (extremely) influenced by the pilot's guess on the best routing (and timing). And that routing/timing may provide hugely different options for the pilots based on their guess on when to start. This is highly chance/guess driven.

These free form, choose your route, OLC type tasks are already 95%+ of US tasking. An assigned task (a real one, not the perverted US rules version which is NOT a race) is more objective but the start time is still a major, often key factor (when pilots of equal skill are concerned). And there are still massive routing decisions which are even more critical in assigned tasks. Only SGP is the only truly objective form of sailplane competition. Chance is reduced by orders of magnitude in SGP over other task types.

Again, in the US today, you have 97% TAT or MAT. Only 3% AT (US perverted version). So those who disagree with me should be ecstatic.