Easy up turbo. Whether the unit is balanced or not is the discussion here. Historical basis simply informs balance by giving the unit context. At any rate, yes, it absolutely should be supported. It's a long range unit, after all. The question is more whether it's a useful unit in its own right.
Your opinion seems to be that it should only be considered an anti-infantry unit, which is a valid perspective. That doesn't change the issue of whether the HE shells should have some effect on tanks though.
This is meant to be a discussion, not a flame thread. Please refrain from needless aggression.
His opinion was clearly that it should not have AP abilities while HE is loaded. Not that it should be only AI as you wrongly concluded.
I agree with him, there's no reason it should be able to hurt tanks with HE considering it can still wipe full health squads with spread out models at long range.
The limit to 1 at a time does not change anything. Back before any changes, 1 was always enough to ruin gameplay by deleting full squads and causing heavy damage to tanks.
I strongly feel your ideas is bad and pray it is not considered.