dont forget the other aspects of shield boosters. A X-Large T2 booster only gets 600 hp for 400GJ while a T2 Large Armor Repairer get 800 hp and 400GJ.

Armor has 1.5 cap/hp ratio while shields have 2.0.

And if your going to compare an ASB to anything do it against the AAR:


The Large Ancillary Armor Repairer does 1350hp for 400GJ (assuming nanites loaded) and does it for 8 cycles (120 seconds)

The X-Large Ancillary Shield Booster does 980hp for 0GJ (again assuming cap charges loaded) and using cap booster 400 does it for 7 cycles (35 seconds)

AAR repairs 10800hp total (90hp/s)
ASB boosts 6860hp total (196hp/s)

So, the shield ship becomes vulnerable within 35 seconds. it's not a matter of 1 being more powerful than the other, it's all reliant on playstyle. armor is more passive and drawn out while shield is quick and fast. With an ASB fit shield ship your hope is to kill the enemy before you run out of cap boosters. With armor, you hope to outlast the enemy and use your utility mid slots to keep him where you need him until he has exhausted his options and is vulnerable.

AS for fittings, it's an opposing situation, Armor needs more PG while shield requires more CPU. Shield fits require more cpu than armor and vice a versa. Along with generally higher resists armor also has the option of the 1600mm plate where shields do not have a similar option.

It's all about playstyle.

But the main reason shields have a X-Large booster is because armor has a 1600mm plate, which gives almost 2x as much hp as Large shield extender.