Well, with strength build... perfected strikes are kinda' shite, most of the time, honestly. Strength deck or otherwise. Heavy blade (upgraded one would have been, what, fifty, sixty damage at +10? Double tap that three or four times and you win), sword boomerang, twin strike, maybe pummel, definitely that one exhaust card (fiend fyre?) are all much, much better if you're rolling strength. Every extra attack the card has is effectively another pip of strength.
+10 is also low (that's like all of three turns of demon form, and basically nothing if you have upgraded limit break), really. End-game strength deck can often break triple digit strength (this entails playing limit break like, three, four times if you have something for them to build off of?) and literally one-shot the time jackass.
... for the rest, it mostly sounds like you're just neglecting defense, to some degree. Eight seven damage lightning shots would probably be fine if you have (echoed) reinforced body or somethin'. If you got the damage, you ultimately want to play as few cards as possible and weather the assault as it dies. Keeps the strength scale under control.
E: if you want an easy-ish defect one, get a source of dark, multi-cast, and some energy gen. Hunker down until you have a shadow bomb big enough to explode the thing in one go. Sixty point boom'll do it from full health if you have six energy, iirc, and that's fairly easy for an end-game defect to have.