Do you dead hang & squeeze at the top with a slow drop down?
Basically asking if you're doing 100% ROM or almost 100%.
Also are you doing perpendicular grip or only regular grip?
Discussion
Regular wide grip and I like to believe I'm doing 100% range of motion and slow drop down
Deadhang at the bottom & stop going wide.
Find a neutral / regular overhand grip.
Also do the perpendicular.
Deadhang, squeeze at the top, slow down.
Also do sets of hangs in both of those grip styles.
You'll overcome that bicep deficiency.