patching a +def/-atk surtr?

The base kit, I'd say. You have a really tanky IV and it's the 20 chip damage plus Peshkatz effect which makes him so hard to deal with. You need to survive a hit to get it off, snd you have a good IV for it. With the bane you still have 60 atk after the buff+debuff, which is enough against a lot of opponents when the 20 chip damage gets factored in.

If you want more atk, keep a drive or a goad around.

That Surtr is fine.
Don't 'patch' his attack, go all out on the def. 47 with just his weapon. 55 with steady stance 4!

Look at Surtr's weapon. Then look at his C skill. Then ask yourself if Surtr really needs his attack all that badly.

-Atk +Def is almost certainly Surtr's best IV if you want 180 BST. If you don't, then obviously -Spd is preferred.

best IVs next to -res if you want 180 BST. tbh, he might be one of the only units that likes -atk since all his other stats don't want to get lowered, along with Kliff. Just build on defense, Surtr's Menace and Sinmara will do the rest.