I think (just assumption, I'd have to do a bit of research to validate this opinion.) that those grips were designed to allow 2-handed operation to overcome aerodynamic forces in the age of no hydraulics or low-pressure hydraulics during relatively high airspeed, high G dogfighting.
https://backcountrypilot.org/forum/w...l-sticks-18303
This reduced the need to hold your arm out so straight to fly which relieved some strain on long cross-country flights. The result of the stick being nearer the pilot necessitated the spade grip so that it could be held at a more relaxed angle and not require you to bend the wrist the wrist so much.