User blog comment:StonerCatJay/Rereading the series- theories and speculation/@comment-3230060-20140522160420/@comment-5551986-20140523174201

Isshin did use Getsuga Tenshou in his fight with White, he just didn't use it on White's physical body but rather his Hollow Soul or Hollow powers corrupting Masaki, http://www.mangapanda.com/bleach/536/3. Dunno about you guys, but his Soul and Shinigami powers were connect to Masaki, but using it after such a short time? I don't think so. And seeing as how Ichigo's Inner Yhwach only used it in fillers is quite contradictory as to whether its a Quincy ability.