Stun Immunity limited to 1-H weapon users is part of the balance of the game so I would caution against tweaking it for everyone.
The stun immunity is the big draw for the Warrior Skill Infantry Training and is restricted to 1-H weapon use to balance out the higher damage output for 2-H builds, which can use Battle Rage to address stun issues, including negating a stun effect that's landed. Note: Battle Rage can also be used by 1-H weapon builds, and when paired with Infantry Training, makes a rather solid stun-resistant build.
Battle Rage also gives increase to STR and DEF, which translate to more damage and more health for most 2-H builds that use 2-H Expert and Body Development).
Edit Note: For clarity, Battle Rage allows escaping from stun and paralysis, Infantry Training makes immune to stun and halves paralysis effect. Thus having both skills makes one immune to stun, able to un-paralysis and failing that, only paralysised for half-time.