Minecraft – How to clear huge area in Minecraft

Try: /execute <selector> ~ ~ ~ fill <relative coordinates> air 0 replace wool

[EDIT]

If you are wanting the block to disappear after a certain amount of time, say, 30 redstone ticks (60 game ticks), you could summon a WitherSkull below the player and use the execute command on it.

To make the block disappear, you would add a new scoreboard command, lifetime, for instance, and run /scoreboard players add @e[type=WitherSkull] lifetime 1 with a setblock or fill clock, then execute another fill command on every wither skull with a certain lifetime value, like:

/execute @e[type=WitherSkull,score_lifetime_min=31] ~ ~ ~ /fill ~ ~ ~ ~ ~ ~ wool 0 replace air.

Then, you would kill the wither skull: /kill @e[type=WitherSkull,score_lifetime_min=35].

Here is a screenshot of what I did:

/clear works fine for me. Try using the vanilla command rather than the one from Essentials, if possible, you do this by using /minecraft:clear.

Alternatively, you could try using /replaceitem with air, like this:

/replaceitem entity @p slot.armor.feet air
/replaceitem entity @p slot.armor.legs air
/replaceitem entity @p slot.armor.head air
/replaceitem entity @p slot.armor.chest air