I haven't seen a unit with "Alliance Defense" or one that I recall - but the last FA Event proved that a defense bonus is currently the most desired prize as we saw many teams purposefully try to drop back and fall into that 11-15th prize range for the 20% Air Defense Prize. First event in MW history that Sup 1 (in one form or another) didn't finish in the top spot.
With that said - I'm betting if in the next WD if Gree placed a +20% Alliance *Defense* Bonus on a bright purple plane - you would see teams from way down claw their way up trying to get it - as in an Epic Gold rush.
How many people have a nice Attack with a Defense stat that is only about 60% to 75% of their attack - THUS creating the issue of raiding a juicy target - and then becoming a juicy speed dial for the person you just hit.
Just saying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .