The problem I see with Swarmers is that many of them could use Area of Effect Immunity.
There are so many mechanics in the game that just garbage dump large numbers of small units, that even increasing their health would only mitigate the issue, not solve it.
Why, for example, do Frigates have AOE immunity? Frigates by definition are supposed to be long-range support units. They can avoid the battle with their high range. Wouldn't it make 10,000x more sense that those small swarmer units which have to be on top of their targets, and who are very susceptible to AOE have the immunity to it?
To me, Space Planes are pretty much the pinnacle of what a "Swarmer" should be. They have amazing damage and multipliers (Heavy, Structural, AND Polycrystal...that covers the most important targets in the game by far). They have Cloaking. They have Radar Dampening. They are Blazing Fast. They can remove key structures from the game extremely well, but also contribute well to a fight if microed correctly. They aren't just cannon fodder, because with their unique characteristics, they add a unique blend of bonuses to your army that it's hard to find elsewhere.
Most other "Swarmer" units do not fit into this category however, because they have no cloaking, and no radar dampening, and they rely on the "brute force" method to be useful. Yet they simply get evaporated by TONS of different types of AoE weapons, and have so little health that it never really works out in practice. Swarmer units need some kind of epic survivability mechanisms like the Space Plane in order to be useful, otherwise they're just going to be an underpowered ship type.