all of this angling of the engine is just to compensate flight which has a significant angle of attack
many of the old designs struggled around and wer a handfull on landing and take off and in a vertical line (well- a steep climb) were slipping and skidding and the props added a fair bit of unwanted forces.
really light aerobatic stuff which accelerates very easily don'tneed any of this angle business actually inmost cases you don't want any of it Now if you are building a Islander with the engine mounted on a pylon (the vertical fin) - you are going to want some angles.
some pattern guys believed (incorrectly) that one could design a plane which flew hands off thry any maneuver and held any line -
fat chance
the closer the model got to THIS condition -the more unstable it became