This is actually untrue.

Every "pro" I have ever talked to or have flown with have mixes setup. Take a look at any of Quiques flight/assembly manuals and he gives you the mixes he uses in them, usually the flight manual and if you ask him he may even send you the backup file from his 10X. Bill Hempel uses mixes on his 14MZ, seen them myself. Chris Maier helped has helped many people setup mixes and trims, seen this in person a lot as I compete with him though not in the same class. Kyle (The Alien) certainly uses mixes though he's that instinctive that I've seen him take a plane on it's maiden and fly it like it already had mixes and trims setup and never touch the trims on the radio.

Most pro's will gladly tell you how they do it, just ask them. Just cause they are really good at what they do, that does not mean they are untouchable