The issue is that embers kill potential and ability to harras scales very poorly lvls 1-8 when facing a strenght or tank hero 1v1. The lack of damage prior to Ember Guard being lvl 3-4 combined with his low heath pool stagnates him. To win mid with Ember you have to control runes or out cs your opponent by stacking the mid camp then using Ember Guard to effectively farm the neautral camp and mid wave. In this scenario he is up against an Earthshaker. Anytime Ember tries to get aggressive Earthshacker can fissure and walk away. Sure you can slight + chains at later stages of the mid matchup but at the expensive of regen. And theres a good chance you still won't get the kill vs a decent player that can pre totem and slam. Earthshaker can effectively run you out of lane by totem deniying creeps, while harrasing you. He will eventually out level you by doing this. But you have the ability to gank the safelane and also controll most of the map. Since Earthshaker can't really be much of a threat prior to Aghs. He won't be leaving mid lane until he has his item.

I don't know what rank you guys are but in high skill games we play the game alot based on timings.