Sure, Kalista may be a bit obnoxious, but this is bullshit. Malphite kept throwing slows at a character basically immune to slows and couldn't catch her. What a surprise. Might as well say "He kept throwing his Q at Kassadin but he escaped, nerf pls", since it's the same.
What could have happened is next: Maplhite ults to instantly close the gap and get some damage. Then follows up with his AS slow. He also still has Randuins and FH's AS slow. Your Malph didn't utilize any of instant gap closers or multiple AS slows which all weaken Kali's passive enough to catch up.
Also, if you got kited that far by, say, Vayne or Lucian, you'd be dead before their backup arrives.