I agree with Red Arrow. I love playing Kalista with high attack speed but mostly because it is insanely fun to kite circles around your opponent.
If you honestly play her like most ADC champs and use her increased mobility to maintain positioning and dodge skill shots you will be a much stronger carry for your team. Her ability to dish out massive amounts of damage along with her Rend ability will shred through HP tanks faster than a heavy attack speed build. Attack speed is obviously helpful, but this is true with most if not all ADCs.
Another important ability for Kalista, which tends to become undervalued toward late game is the Soul-Marked Passive part of her Sentinel (W) ability. This can deal up to 20% of a target's max HP once per 6 seconds. Six seconds is a long time, but it can really soften up ANY champion followed a single crit auto, Pierce, and Rend to either finish them off or send them running. Even with low attack speed her slow along with her passive mobility will make it easy to chase them down and finish.