Note that this frees up design space: for instance, APCs might have lower HP than a tank, but compensate via no (or fewer) weak spots (as befits a vehicle used for infantry/urban support)

And the HAV weakspots don't have to be a full side. For instance, perhaps the bonus applies to the rear half of the side, but not the front half.

In any case, racial AV would not hinder this system from working. We could perhaps even give tanks a damage resistance to being hit from the front as suggested by Adamance. But the point is, AV is taking a nerf, but this gives them that damage back, while requiring tactics instead of module stacking to achieve that damage. This makes for a more interesting battle, where AV could let a tank pass to get a shot at it's weaker backside as opposed to opening up on it where it's defenses would be strongest. (ie: the front)

This also aids swarms, as unlike forge guns, you cannot decide exactly where on the tank you are going to hit. Which means that hitting the weakspot of the tank is way more about luck than any kind of skill. This gives them the ability to get in on the bonus damage that currently can only be consistently applied with forges.

I'm actually in favor of giving a damage resistance to the front of an HAV. Would give tankers the ability to benefit from positioning, while simultaneously giving AV a reason to flank them. This in turn give tanks more incentive to fit small turrets, in order to cover their weaker areas.

True, this is why urban environments are so deadly for them. I never worked directly with armor, so I never learned their specs. In any case, I think the concept is sound. AV gets a nerf, but can regain that damage with good tactics and positioning. HAVs can counter with their own positioning, making skill a little more important than number crunching.