Because they chose to register for an Open division at a DGPT event despite not being that level of player would be my first answer.
Yes, that's an issue. But this course was too hard for even the top-rated FPO players. (Besides, FA1 in the companion event played an even longer course.) Total par of 71 was right for FPO, but playing a true par 71 course is a grind for most people. On top of that, the scores were tilted more heavily to tough pars than easy pars.
How are you defining "fit"? IMO a course "fits" a player based primarily on a lack of shots that said player is simply incapable of executing. Simply looking at the scores paints an incomplete picture, particularly on multi-shot holes.
The measure I use is based on how well a course lets the players get the same mix of scores as 1000-rated players get at ES+ events. This means not too easy, not too hard, and not too many of the same score.
It's true, I make the leap that two players getting the same mix of scores are having a similar experience. Scores can tell us a lot.
In this case, we can see that 930-rated players have only about a half a chance of getting a two during any round. That means the 930-rated payers aren't capable of parking many - if any - holes. So, we know that the course took away almost all the chances to park a hole from the tee.
I was admittedly surprised at how poorly the lower rated women (the aforementioned 875 players) played holes 13 and 14 in the event. …
It wasn't just the lower-rated women; holes 13 and 14 played as one higher than the assigned par, even if only the 930-rated players are considered.
Compared to the MPO course, the FPO course was about 88% as long. This is longer than the 75-80% recommended. A good start would be to add (or use) short tees for all the holes. (That's
after re-thinking whether the par 71 Blue course was too difficult for MPO.)
As to the original question: I don't think difficulty is over-rated yet, but it has now become possible to have courses that
are too difficult. Blindly adding difficulty is no longer a sure-fire way to improve a course.