That depends on the stick. It may or may not be easy to get both hand on it and generate the force necessary.
I know several P-38 pilots who said the yoke and column reduced effort considerably, and made it a lot easier to get maximum deflection.
I also remember one of the P-38 pilots, I think it was Art Heiden, who said he went through a hole fight with one hand on the yoke, because the circuit breakers on his props kept popping, and he had to hold them in with one hand.
By the way, with regards to the comment about the yoke hitting the kneeboard, there is speculation that the pilot of the Duxford P-38 did just that, and it caused him to crash, killing him and destroying the plane. Odd, I can see where a combat pilot on a mission would need or want a kneeboard, but I can't see where a pilot flying local VFR and performing aerobatics would want one.
I've seen Steve Hinton toss "Glacier Girl" around VERY hard (a HELL of a lot harder than you'd expect to see a one of a kind 6 million dollar P-38 get tossed around) and talked to him afterwards, on several occasions. One of the other guys did the same thing to "Porky II". Neither of them had anything other than tennis shoes, coveralls, and a helmet. And after 30 minutes of HARD flying, in the hot sun, neither broke a sweat.