k mate, you seem to get all on tears, calm down.
I played cass 10 games on this patch and didn't lose a single one. if ap miss fortune doing better that the current cass riot's balance team should really take care of her, might be the next Warwick of soloQ.
her E range is higher than the autoattack range of most ad carries, and it seems they are perfectly fine, so is cass.
as build goes, seraph's, rylai and hourglass working just fine for me, and if you really need more defense you can get another defensive item to finish your build as you already hitting over 1k ap.
poison matches a snake, but that's exactly it, the gave to her DoT a fitting name, nothing more than that.