Asmala, 2 SD would have to always hit for them to be effective in reducing the defensive strength of the phased shields below that of organic armor. If they miss, then they do not reduce the strength at all.
Taera... as Asmala said, that is not really true. Keep in mind that you will be able to support maybe 100 ships to my 95... the costs are not that much different. In fact, organic weapons tend to cost more than regular ones do (comparing similar weapon types, of which PPB is not one, as there is no shield-skipping organic weapon). Unless you use huge amounts of defensive components, this balances out the cheap cost of OA, leaving your ships costing aboue the same amount of resources. Again, unless you have only a few weapons and a lot of OA, in which case your ships will lack the firepower to do any real damage. Remember, fleet stacking means that your OA will not get much of a chance to regenerate for most of your ships. Sure, you can build them faster, but so what? You still have to pay for the construction and maintenance on all those ships, which is about the same as for a "normal" player. When you factor in the necessity of training your ships, the effective "build time" is increased by 7 turns (to get 20%, you can go with 18% for 6 turns if you like). So 11 compared to about 9 or 10. Not that significant. Forgo training and watch your ships lose horribly.
Of course, you can always use the exploit and use a huge planet with 2 moons to get 3 training facilities, which leads you to 7 turns or 5-6 turns for max training... still not very significant.