I believe that Ford's prime reason for going to turbocharged V6 power in the F150 is the EPA fleet fuel economy requirement. Given that, I think that the likely reason for putting the EB engine in the Raptor is that if they didn't, it would call into question the whole EB campaign - which would be bad PR and bad marketing.
If I'm right, then sound automotive engineering is a secondary or tertiary consideration in the overall concept of the 2017 Raptor engine. One might expect, therefore, very modest fuel economy improvement or perhaps even none at all.
I also note that while Ford is currently claiming that the 2017 Raptor's EB engine will produce more power and torque than the 6.2L V8, that's all they're saying. They are NOT saying how much power and torque the new engine will produce. I think that they're still working on it, that they don't know exactly how much power and torque the new engine will produce, and that exceeding the output of the 6.2L V8 is merely a design goal.
We'll see.