Hearthpwn

One minion like 3 manas 3/3 battlecry "If your opponent have 4 or more minions destroy all minions" will be much powerful? I think the game should have more tools vs the strategic too dominant for a long time, play many minions fast you can and win the game in turn 5 or 6.

We have MCT and Doomsayer but is not reliable and don't solve the problem in many cases, why so poor resources vs aggro decks?

A neutral mass removal would be nice. But a 3 mana: destoy all enemy if the controls 4 or more would be broken. Super broken actually. 

We need this, and we need class removal to keep up with grossly overpowered neutral minions. 

Because aggro decks are good for the game in so far as they:

a) Are cheap to make thus retaining f2p players,
b) Have a low learning curve so are noob friendly,
c) Keep the average game time quite low, which is a priority for Blizzard
d) Stop everyone and their uncles from playing the greediest possible lists in the world

We have plenty of tech cards to deal with aggression more often than not.

Some classes have pretty decent mass removal vs aggro, but you can't just give mass removal to any class otherwise everyone would just play control instead.

There are just some classes that are better for rushing down your opponent (i.e. Hunter) and others that are better at controlling the board like priest or mage (or even paladin, if you consider equality + consacration/wild pyromancer)

Because Blizzard doesn't want all decks running the same Neutral anti-aggro cards, that would defeat the point of having different classes in the first place. Plus, I'd argue that control decks are actually stronger than aggressive decks at the moment, if those aggro decks don't high-roll into an early Prince Keleseth. Giving all control decks even better anti-aggro tools would tip the scales too much.

I don't want a meta where it's all control, that would just be the inverse of the problem we've had for years where aggro has dominated every single meta.

Not really. Aggro will always be aggro and people will always try to build aggro decks as it is usually cheap and an efficient use of time when laddering. We can have creative ways to manage aggression such as the aforementioned MCT and Doomsayer. Taunt creatures are also a viable answer to aggression. But a generic board clear like you proposed will not be healthy for the game as it dilutes the viability of other cards, deck archetypes, and class identity.

If you're targeting aggro decks, then the best solution I think would be to use a class which has those tools like Mage, Warlock, Warrior or even Priest.

Neutral Board Clears:

Unstable Ghoul, Deathwing, Doomsayer, Explosive Sheep, Corrupted Seer, Abomination...we have plenty of these.

Fight broken with broken?  No thanks.  Just stop printing garbage like Bonemare and Cobalt Scalebane

ghoul - wild only

deathwing - lol 10 mana board clear, ok

doomsayer - common to be able to deal with it as early as turn 2 these days

explosive sheep - wild only

corrupted seer - turn 6 2-dmg aoe is a joke and this card sees no play whatsover

abomination - 5 mana 0/1 frog with taunt

we have.....no good neutral aoe

Neutral mass removal should be slightly over-costed/under-statted, due to the fact that all classes have access to the card. That's the point of having it Neutral, not to stop aggro decks from happening. I assume you're talking about a non-Legendary, since we have Deathwing. Since we don't yet have Neutral spells, it would have to be like a 7 mana (perfect follow-up to Bonemare) 2/2 minion that wipes the board and heals your opponent for each destroyed or something like that.

I think Blizzard prints many non-mass removal Neutral minions on purpose. Cards like Abomination, Doomsayer, Corrupted Seer, and Primordial Drake all have "conditions" that need to be met in order for them to clear the board. I think this is the pattern they will stick with in the future as well.

Quote from Kaladin >>

abomination - 5 mana 0/1 frog with taunt

It's common to be able to deal with a turn 2 doomsayer? What combo of cards easily does that?

Deck hand + patches turn 1 into flametogue (that's viable)

devolve (you don't establish a board)

shadow word: pain (again you don't establish a board and then the next turn your opponent plays a 3 drop which kills a potential cleric for free)

manaworm into glyph, gryph, frostbolt (hardly realistic)

Hunter's mark (assuming a hunter is playing this and got it in his opening hand and developed a one drop)

crackling razormaw into poisonous on a 1 drop (if you want to roll the dice)

backstab + eviscerate + 1 random attack from dagger or 1 drop (all that to kill a t2 doomsayer)

crazed alchemist in wild aggro druid ( feasible)

Fell free to spot me some more but it doesn't seem that common to be able to deal with doomsayer on turn 2.

"as early as" but you don't just slam down doomsayer on t2 just because it's a 2-drop.  my point was that doomsayer doesnt really get the value it should anymore because generating additional damage from hand is way too easy.   

Aggro doesn't balance meta, it's the issue. In times of turn 2 (coin) with 3 murlocs 3/2, 3/3 and 2/3 = 16 stat points or 4/1 DT: 3/2 and 3/2 beasts = 15 stat points you need more solutions. Flame juggler was a former aggro card with 2/3 + 1 random dmg. Nowadays it's a joke. 

Anduin, Jade Idol and co. are the issues on the other hand.

We have a game with power creeps. Good old value yeti and minion trades are gone with hs Identity. So play aggro or control power, scissor paper stone, and that's balanced.

No additional removal

Just play more high value taunt if you hate aggro so much.  Tar Creeper, Second Rate Bruiser, Saronite Chain Gang, etc go a long way to shutting down aggro floods.

Completely on board with them printing better neutral board clears. As for OP's suggestion of the nuclear Mind Control Tech? Not so much.

Quote from Kaladin >>

ghoul - wild only

deathwing - lol 10 mana board clear, ok

doomsayer - common to be able to deal with it as early as turn 2 these days

explosive sheep - wild only

corrupted seer - turn 6 2-dmg aoe is a joke and this card sees no play whatsover

abomination - 5 mana 0/1 frog with taunt

we have.....no good neutral aoe

I'm done.  Continue being wrong. 

There is a nice balance between aggro, control, combo and midrange decks at the moment. We don't need too many more anti aggro tools at the moment when Patches is about to rotate out. Without Patches at the moment aggressive decks wouldn't see any play whatsoever and would probably be worse than the state of hunter, we do not want this, it will make for an unhealthy meta. 60 minute fatigue games every single game do not sound fun to me.