I have not competed in EBR, but, will offer a quick opinion.
To win at EBR, you must remove every detail that could interfere with the accuracy of your shot. Pellets are the most variable of any component, other than maybe wind. Wind you can't control, pellets you can.
Tom Holland has an entire video about the prep he goes through for Field Target (Field Target Tech). Washes, Dries, Inspects, tests by rolling on a sheet of glass with a square to ensure the skirts are good, weighs, lubricates, basically does anything he can to make sure the pellets are uniform.
I've tried his methods, and they don't take all that much time when you consider the investment in competition practice and such, plus, I've seen a difference. Just eliminating the super heavy pellets or super light pellets (example, my 33.95 gr JSB pellets in .25 can be as light as 33.00 and as heavy as 44.6 grains). Just eliminating the variance at that level makes a difference. For me, skirts and head size are less of an issue due to the FX Smooth Twist and the way it reshapes the pellet in the barrel. Pellet comes out in a fairly uniform pentagram shape rather than round.
In my Marauder skirts are a bigger issue. I still inspect skirts in all calibers to give me the best chance at a good store.
From what I've seen, (remember, not been there), anyone serious about winning does the pellet prep as it's the one thing you control that has the most variability, and can effect your shot accuracy the most.