The shield can provide cover from grumpy bomb allowing you to avoid the stun.

use the payload cart to help shield yourself from his flame attack. Does not totally shield you but can be used to close in or aid in escape.

take out the turrets. nearly all good Barik players use the card that lets them gain healing from there turrets

It is possible to stun him and kill him in ancient rage. So any crowd control ability can pin him allowing you to either move away or let the team focus damage on him.