In my opinion, Flash stuff with the Octopus is more related to range than anything else
We all know Attack Potency doesn't mean Range, Flash can't nuke a small country, his range is, literally, an extented melee range, therefore giant opponents may be a little harder than expected because you are hitting them with potency on a small area, destroying a small part of their body and (quite likely) not one shoting them
Flash not only had small range against a multi-building sized monster, but was also quite casual and only going for the eyes, the fight was interrupted, so there is 0 reason to look at it as shameful for him or some sort of anti feat