Not all are of that stripe. For example, McClelland Barclay was killed when his ship was destroyed in the South Pacific during World War 2. Dick Calkins, the first Buck Rogers comic strip artist, was an Army Air Corps lieutenant. And some artists for 1930s aviation comic strips were pilots.
One pilot-illustrator was Clayton Knight (1891-1969) who was shot down on the German side of the front lines during the Great War. Before the American entry to World War 2 he, along with Canadian ace Billy Bishop, was involved in recruiting American pilots to fly for the RCAF and RAF.
Biographical information regarding Knight is sparse on the Internet -- here is a brief account. For a detailed report on the World War 2 Clayton Knight Committee, link here or, better yet, here.
Today, if Knight is known for anything, it is that he was the father of Hilary Knight, who illustrated Kay Thompson's "Eloise" books.
Here are some examples of Knight's work.
Knight's illustrations were mostly aviation-centered.
Rickenbacker got the credit for the strip, but Knight did the drawing.
Here we see knight's signature.
Knight sometimes was able to hit the big-time. He might have gained this Post assignment because he was typed as an aviation specialist.
These planes are not skillfully depicted.
The Townend Ring around the motor is slightly too large.
Based on the illustrations above, I have to conclude that Knight's work was at the journeyman level, far from top-notch even where aircraft were concerned.