Well, I think both may be kind of true. When you are considering competing at the highest level, maybe everything is "a thing".
I've been involved in the shooting sports for over a half century, rifle, pistol, shotgun, air gun. From my experience, two things are consistently true about the champions in all disciplines. One, they practice hard, and are very good. Two, they are a little nuts. I don't mean that in a bad way, they just focus on every little detail, and the cumulative effect of all these little things adds up and builds confidence. Does washing pellets make a difference for 99% of us? I doubt it. But if you think it helps, then it does.
When I got into reloading I started with the very basic RCBS rock chucker kit back in 1989. Very basic kit, so my loading knowledge was just as basic.
Fast forward to 2012 when I read Glen Zedicker’s book on hand loading for competition and that turned things around for me. The perfect hobby for the ones with the OCD. Everything he suggested and bought for tooling, I did exactly the same.
Then in 2017 when I discovered PCP’s, the lessons learned from precision reloading carried over. Sorting, weighing, and yes, washing, checking things with calipers, pellet gages, etc, etc.
Here’s my take on it- if I’m going to spend hard earned $$ on quality Ammo, and I know of methods that will help my accuracy(because I’m not a great shot), or make factory Ammo better, I’m going to do it. If I miss what I’m aiming at, I want to know it was my fault as a shooter, not because of Ammo, my gun, or any of my equipment.
Oh yes, the gun. You think pellet washing is tedious? Chase accuracy just in your equipment, and that’s what turns this into a full time and expensive hobby.
The most important thing, though, is to make sure you enjoy all and whatever it takes to chase hole in hole groups