Your number is way too low. I have 16 defensive wins and I have a pretty junky deck (2 level 100 SR MOEs, a level 100 R MOE, a level 61 R MOE, and a level 86 SR Sexy). Because I tend to be a completionist and like to max out the cards I'm working on and didn't realize that Sexy's were a better choice for that strategy when I started it. With a better array of cards and ability to make a real trap deck, I'm sure I'd have quite a few more. Nowhere near as many as some, obviously, but more.

I'm trying to figure out when the day resets. It apparently does not reset during the time period when missions reset? I did a few attacks this morning, and then when I got back this afternoon I was at 0 daily completions...

Edit: In addition, with this deck I have a winning streak of 112 right now. So lower decks can do just fine attacking lower-ranked people (I have just been going after Rank 3's).