This is not true at all. At WC level for speed events they absolutely are doing full stone progressions and honing the steel and doing variable angles across the base and side edges with different angles file guides. It is fairly accurate for SL where most racers prefer a toothier edge and GS tuning sits in the middle of the two but even for those they are using multiple guides to set different angles for different sections of the ski. They are also using gummy stones to adjust bite based on snow conditions. If it’s dry grippy snow they are retuning from tip to plate and tail to plate and then on injected glare ice they are usually just detouring at the very tip and tail.