I think this post is a bit of an exercise in think out loud - or rather typing - but I really like the community's speculation and ideas.
When the defender was finally announced I was really pleased; it's probably my favourite ship because of the fond memories of hours of Tie Fighter gaming on the PC. I love its stats and the cost is steering users to a smaller imperial squad ( I have no problem with that, the variation is cool). I feel that the defender is a ship that is being 'short changed' as the game stands at the moment:
In order to get Rexler's ability working focus is needed, using his action to get that focus really reduces his potency as if you want to flip damage then the other actions are redundant. I can only see Vader as a real option to help supply the focus actions through squad leader. Soontir Fel would be wasted having to hang around in formation if one put squad leader on him - as would Vader for that matter ( let's put cost of Vader aside for now).
Where do you suppose a focus generating ship/pilot/upgrade/ability for the imperials is going to come from?