I am not sure that is a bad airfoil. A wing section must do three things...
- Generate lift, generally equal to the weight of the aircraft
- Generate minimum drag
- Work as an efficient structural section.
That third item became particularly important when cantilever wings were developed during WWI. A thin wing section is a functional structure if the wing is a set of short cantilevers supported at both ends. If all the attachment and support is at one end, the wing must be way stiffer and stronger. Early cantilever monoplanes needed to be very light, so the wing sections needed extra structural efficiency. They needed to be thick. A thin cantilever section must be heavily constructed. On a 400mph aircraft with 1000+HP, this is manageable.
Thick airfoils were not well understood back in the day. The figure is what I call a Bernoulli airfoil I analysed it at zero angle of attack, using Bernoulli's equation. It works. For an aerodynamically efficient shape, you need to round off the leading edge, and move the top of the curve to about 1/3 chord. You wind up with something that looks a lot like a Clark_Y airfoil. By WWII, newer, more symmetric airfoils that could not possibly work by Bernoulli's principal, were developed empirically in wind tunnels.