Don’t grip the bars so tightly and don’t feather your brakes! Just rest your hands on the bars, you don’t need to grip them, you’re trying to control a big gyroscope that wants to go in a straight line, so don’t grip tight and fight it!
Also riders tend to ‘feather’ the levers, just taking up the ‘slack’ before the bite point. Adjust the bite point better and let them go and just brake when you need to!
All the above suggestions can work, but they are not THE solution, you need to try and find yours. I have never had arm pump and use thick grips, Ali bars and two finger braking coz that’s what suits me and what I’m used to my MTB’s and motorcycles.