For nearly 99% of the gym training world, the key to bigger bicepts is in increasing the big lifts like deads, squats, presses, and rows. These drive long term progress and major mass increases. If there was some magic combination or amount of isolation work the noddle arms curling in the mirrors and using the power rack to hold their curl bars would have certainly lucked into it by this point. Direct arm work basically fluffs out and incrementally develops the base one already has. As for increasing the base, that is done with the big lifts, even the ones that seemingly don't involve arms like the squat. Put 100lbs on your squat and dead and 50lbs on your rows and presses - you will find bigger guns.