No, but Indirectly yes - mainly when your gunner reload time (“maintenance”) is too long and you have to reload at the most inconvenient time.
So imho the most decisive crew XP for defensive armament is the gunner reload time - at least for Air RB.
Having reload times of 10 seconds can decide between life or death. 10 seconds from initial 40 seconds for a level 75 crew in an aced aircraft is a game changer in certain aircraft like in my B-18 B. If you fly with a Hotas and with “auto pilot off in gunner view” you can even roll and fly inverted to use the other turret until the first one has reloaded.
The XP for defensive armament are imho borderline useless as they just shine when it is too late, meaning that your attacker came into his effective gun range. But technically seen they are not really effective.
There is still this hoax that auto gunners would open fire at 0.21 km distance - this is imho flat wrong even as mentioned in the stat card. The “real” value is 0,66 km - and it depends on which way the barrels are pointing at.
So if you attack a B-25 from 12 o’ clock high the barrels of the upper turret are pointing backwards - it take too much time to turn 180° degrees. If you perform a dive attack from 6 o’clock high the barrels show already towards you, so chances to get hit by auto gunners increase significantly and depend on your excess speed. That is also the reason why a hell of bombers with bot scripts had thousands of losses but depending on the plane also hundreds of kills.
The only exception from this rule are the few actually skilled P-61 pilots with level 75 crews and aced planes. They are using the imho way too fast turret rotation and the very effective auto gunner in an offensive role whilst scissoring with enemy fighters. Every few hundred matches you meet on one them. That’s why i always check stat cards before i attack a P-61 :-)