Hi!
Have been in this sport/hobby for 34 years and I don't use a mixed throttle /rudder on any of my planes! Be it sport planes, pylon racers, scale or 50cc gassers! At take of all my planes track straight forward!

When newbies complain about a plane not tracking straight they always tend to think about torque /P-factor, but its not!
The reason some planes (mostly belonging to newbies) do not track straight is that the wheels on their planes are not set up correctly!