This is what my relic 5 - 7 is experiencing.

Basically, what MasterSeedy said.

As you know, EP Empire teams are runaway TM trains and stun trains, and once they get their debuffs down, you might not get another turn (unless your counter has specific ways to stop them). 

Also, mirror matches notoriously often come down to whichever team is faster, especially so if the teams are TM trains. And in Conquest, the enemy teams usually get huge artificial stat boosts, including speed. 

Note also that daze, which Admiral Piett applies, shuts down bonus TM. So unless you can be certain to get the first turn (usually with Vader), then an EP team is an especially bad team to counter EP with Piett.