Well, he was the bloke who made it work effectively, I think he deserves the credit for that. (Or at-least he employed the people who did.)
After all, there were many people who discussed how to make a flying machine work, but it was Wilbur and Orville who get the credit, since they actually made it work. Equally, we're very polite about Leonardo's efforts, but Sikorsky gets the credit for a working helicopter.
The fact is, nothing is ever one person's work in this game. RJ Mitchell didn't design the Spitfire without a team of talented people beneath him, and the experience of numerous other designs to draw upon - but he still deserves the credit.
G