First Clarification: "Good tanks should not be soloable by AV"
I'd like to first state that it most definitely should take several AV to take out a very good tank.

In EVE, assuming players of equal skill, a frigate will never be able to bring down a battleship on its own. But depending on the fit, the battleship can take out the frigate with drones and proper e-warfare. However, a swarm of frigates will be able to bring down the mightiest of battleships.

Now, the flaw with this argument is that you are not limited to player numbers while in Dust you are. But let's take this up to a fleet battle. Both fleets have a call to arms beforehand to muster as many participants for the battle as possible. Each fleet is stuck with the amount of players that showed up and fleet member count is extremely hard to change at a moment's notice. Let's also assume that both fleets have equal player counts.

Each fleet also has certain roles to fill: logistics, ECM and e-warfare, scouts and tacklers, and finally the snipers and brawlers. Both fleets are limited to how they can designate their roles. If half of the participants specialize in non-direct combat roles (logistics, ECM, etc), then half of the fleet is limited to direct combat roles.

Both fleets have some flexibility in how they designate roles and assign ships. When they meet up, they are fighting with what they have. However, say fleet A brought in three times as many supercapitals as fleet B. Chances are, fleet B is screwed.

Dust is actually very similar, except on a much smaller scale, with teams limited to 16 players each. Both teams have roles to fill and are limited on how they can fill those roles based on what people are specialized in.

Tanks are just the equivalent of supercapitals while AV is something smaller. They can be brought down, but requires more than one AV. Just like EVE, engagements in Dust should not be balanced on a 1v1 basis. I do agree that tanks are too cheap now. AV should be considered disposable while tanks should be considered as more permanent investments (1 battleship vs several cruisers; each individual cruiser is disposable while the battleship is not).

In other words, if the other team brought more tanks than your AV can handle, then you should be screwed, sorry.

So the next time you think that it shouldn't take more than one person to take out one person, then you're wrong. Just like a heavy suit, it takes more than one medium suit to take it out (if balanced properly).

Second clarification: Using correct AV for shield
I hear a lot of complaining from swarm users that they can't do anything to a hardened shield tank and it just passively recharges through the damage.

First I'd like to state that the shield recharge mechanic is working as intended.

Now let me explain why it should be like this. Shields are burst tankers with high regen for short periods of time. Armor, on the other hand, has a low regen but higher raw HP.

In order to take out shields, you need a high alpha weapon to disrupt the regen, otherwise a weapon with a high consistent DPS isn't able to disrupt the regen.

Let me go back to EVE. The only way in large fleets to destroy the enemy logistics is through high alpha damage. That's where snipers come in. Logistics can adapt quickly to high but consistent DPS. Reps can get applied in time before enough damage is dealt to destroy the logistics. However, snipers provide high alpha with which to destroy the logistics before reps can get applied.

It's the same in Dust, except shields take this philosophy. A weapon with high DPS but high rate of fire (so low damage per shot) shouldn't break through a shield tank unless there is enough damage being dealt. However, even a weapon with low DPS but high alpha will break through a shield tank. Swarms, because they consist of multiple missiles, don't quite fall as a high alpha damage weapon.

So the next time you try using swarms against a hardened shield tank, just remember that you're using the wrong weapon for the job.