Scarabs not dieing and are overpowering.

There are a couple of ways to counter Scarabs: One is killing them whilst they are moving (since they can't attack on the move) and two is to spam cheap units to let them die to them (since Scarabs sacrifice themselves when attacking).

In regards to health and DPS, level 9 Scarabs have 1.506,4 DPS per unit, meaning they are able to kill 3k health units with their double attack. Apart from that, they leave fire behind, which will slowly do damage as well and possibly kill any unit standing in it with little health left after the original attack.