The advent rebels aren't overpowered. Quite the contrary, the advent rebels seem to be one of the best factions for multiplayer, for people who prefer to play as advent.
The eradica, like the rest of the titans, isn't something you throw close quarters combat frigates at. You use bombers to beat up titans safely. And yes, by the time a lvl 1 titan comes out of the construction yard, you will have enough bombers to kill it in a reasonable tactical time frame, assuming you have been preparing yourself properly. You kill that titan and then destroy its construction yard with your bombers.
Also, if you are playing as advent, a guardian with repulse can often save the day against an enemy eradica.
Wail of the sacrificed is a very situational ability that is powerful when executed properly. It is also predictable, and your opponents capability is easily ascertained by doing some quick, simple scouting and doing a lab count. Naturally, after a while play as if your opponent has the wail anyways, as you never can be to sure if they rush tech to wail or not. Sometimes this playstyle will net you short term losses, just prepare yourself for those losses as best as you can, and try to guess their strategy so you can trap them in a disadvantaged position.