I don't know if I can use this LA!Hector

Of course he's still usable. IV's shouldn't deter you from using a seasonal unit.

No, his Atk will be way too low to be effective. He’ll struggle to land crucial OHKOs

He already has wrath for massive special damage. -Atk is nothing an Atk +3 seal won't patch up.

I used a -Atk LA Hector for a while and he still wrecked everyone. Even with a bane, his attack is equal to OG Ike and 1 less than Zelgius or OG Hector.

I got him with -Atk on his original banner and he's still incredibly deadly. A bane is only -3 to stats and when it starts as high as his he'll still be hitting very hard.

Put Bold Fighter on, He legit has no problem even with a -Atk. Like comeon his attack is still over 50.