AR defense win/loss ratio?

That sounds decent to me. I typically only get one kill on defense, saving 20 lift per day. I think, since it is offense favored, it's best to look at defense as saving what you can salvage, and letting the rest go. Getting 1-2 kills pretty consistently is good enough. Success almost every time is a whale privilege, so unless you want to +10 a Surtr with Distant Counter and support units for extreme delaying, you shouldn't expect much of your defense teams.

You can look up some templates for easy defense teams to get to a decent level and get 1-2 kills consistently. The one I use is the standard Spring Breeze horsey emblem x3, dancer, Aversa debuff trap. Swordhardt, normal Rein, Veronica, Olivia, and Aversa. Makes for a pretty solid team in the upper right corner that's difficult to approach, since they all cover each other's ranges and prevent safe baits most of the time. Except from +10 Surtrs, because that's broken and a hard counter to almost everything.

I think that after a certain tier you should stop hoping for AR defense wins unless you can afford to whale, and instead focus on overwhelming offense. Few things are as satisfying as watching a blue physical unit punch a hole through "the strongest armor in the game".