One thing i have noticed is that defenses do not always seem to impact the outcome of combat as you would expect from looking at the raw statistics.
Sometimes i encounter circumstances and i have to scratch my head and wonder why the hell i should not see a 'victory likely' pop up?? Why? WHY?
Fuxxx me???
The moral of the story is that you cannot trust your strategy too much on defenses...... these days defenses are the last thing i bother researching, whereas in Galciv2 it was one of the first things i research, and actually worked!
I do however research support defenses, which means you can have one support ship giving all your other ships some free defenses.... combined with carriers, its brilliant!