Rebels capturing a prototype Death Star is a whole film worth of plot.

Back when I suggested the Emperor taking Luke to a surprise Death Star and having the two fleets stuck between the two battle stations I thought it through and it could be done with a tweak to the existing footage.

Why on Earth would the Rebels bring their fleet to such a risky winner takes all game if they had a Death Star of their own?

Personally I think the idea of going straight to Coruscant is also problematic.

That would be a few more victories down the line at least.

It's logical they would build one Death Star somewhere remote to make the cover story plausible and lure the rebels in with a weakened Death Star and then pick them off with a more complete one.

When the Emperor's disregard for his own men becomes obvious have a few mutinies to prove that not everyone in the Empire is beyond redemption (which is the lesson of the final picture what with Vader etc).

Having the Executor become a burning arrow plunging into the heart of a Death Star rather than pop on the surface like a dropped slice of pizza gives that beautiful ship a better send off.

It also give Piett, a nice arc which mirrors his direct superior but that's just me.

I'm sure Ady and the team have tonnes of more interesting ideas which play completely differently.