I've got this ship... In general, I don't like it that much, except for its higher DP than L2.

Personally I'd suggest you stick to your L2 because DOE and L2 have the same range, but since DOE is a higher level ship than L2, your exp gained will be lower than exp gained from L2 given the same damage you make. 

Moreover, DOE seem to suffer from shell damage bug. I tried twice landing a full salvo (9 shells) at full degree (40) onto a USN EBB Washington, and the damage made was 30k, which is kind of a joke...

However, DOE shells can do tramendous damage at lower angles (<=25), which means the best set-up for this ship is 2-Gun AW.

Is the shell damage bug related to the gun set or the ship?  Ie., could use use the L2 guns instead and be bug free?

Any bug would be the guns. A ship bug would not affect shell damage in any way.

However, the DOE has far less gun space than the L2, and can only fit 2 binds with L2 guns. It would instead use the cloned ones from the Temeraire.

As far as the DOE is itself, it's a larger (aka: easier to hit) L2 with an option of slightly shorter ranged guns with (in theory) slightly more hitting power. That's it. Since the L2 already has BB6 supports, one of the main benefits of the tier is lost, and what's left would need to have something more interesting to be worthwhile.

IMHO, only the California, Thermidor, and Proletariot bring anything interesting to the table, and even those would only be recommended if you have tons of honor medals stockpiled with nothing better to spend them on.

I am disappointed that the DoE cannot mount longer range guns.

Has anyone else thought about the aircraft catapult on a DoE?  As it stands, all planes launched would crash into the rear gun turret and there is no hangar to store the aircraft.  A more sensible position would be in the gap between the funnels.