Last mission of OG?
You must be on Ryusei route. If you're going for the skill point,
don't bother too much with the small fry and focus on bringing your group in the boss range.
If you have SP Regen, you might want to use a few spirits on your way too.
In any case, when you have enough people in attack range, attack, attack, attack.
If you have people with the attack support skill, make sure they are in position to use it.
I wouldn't be surprised if the boss actually run out of ammo for one of its attack.
Make sure to have units positioned in the blind spot it might leave then.
As for HP regen, what it really means in Super Robot Wars
is just that you must keep keep the pressure on.
That being said, if the boss have the Potential skill
and that it becomes a problem toward the end,
use Fury to override it.
Actually, consider using Fury and Armor Breaker at the beginning of turns.
It won't go to waste. ^^
In lot of case, when I saw difficults stage in Super Robot Wars,
I was often "Aww, come on, do they expect me to go through this?!
Those guy were bosses in the previous stage!" X D
But often it's not that bad when you actually do it.
In OG, I was usually able to go forward as much I could not stopping,
attacking the opponent as we got into each other range.
SP Regen was allowing it, being able to cast stuff like Focus every turn.
Anyway, if you're not going for the skill point, just do it slowly and clean the trash.
Use the Spirit commands of those with SP Regen to gain morale, heal, recover ammo,
give SP to those without SP regen and lower the boss's morale.
It's a general effective strategy through the whole game.
Then, force the boss to make it use it's Ammo attack until he run out of it.
Replenish yourself, lower the boss morale, recover your SP.
Then, unleash all you got on him.
Abuse blind spots left by his lack of Ammo.
You could also consider draining his EN at this point but that might be overkill.
Good luck. ^^