People have been crying about how weak Ashe is for the longest time when, in reality, she IS fine and the only thing that needs changing is her rather worthless passive.
The exact post you just made has been getting made for what seems like centuries, just with different ADCs shuffled around to compare her to. These exact posts were being made back before C9 showed up and started using her. Guess what? Even despite everyone QQing about how shitty she was, a competitive team shows up and proceeds to dominate with a supposedly shitty ADC. She hasn't suffered any nerfs since then.
Kalista's utility is NOT superior to Ashe's. This is just an example of the boards habit of exaggerating everything to make their own points, but no. Kalista's ult doesn't have nearly as much range as Ashe's ult, and it takes 2 people for Kalista to use her ult. Kalista does not have a perma slow. It's rather easy for a champion to stay out of Kalista's scouting ghost vision range. At worst, it might force a ganking jungler to take a longer way around. Kalista has better mobility and better damage, but her utility is not better.
Caitlyn, Kog, Trist, and Twitch beat every ADC in the range department. This is a strength that is specific to those champions, and not a weakness specific to Ashe. Graves loses in range to them, as do Sivir and Jinx. Lo and behold, Graves, Sivir, and Jinx are all insanely strong. Notably, every single one of these champions with huge range were around back when C9 was dominating with Ashe. Obviously that didn't matter.
Her slows are not useless. Not as useful as they once were, but if Ashe's team has an advantage, whatever target she's hitting is fucked. It's pretty easy for Ashe's team to get an advantage considering she has a method of initiating fights on her own. The only other ADC capable of doing so is Varus, and his doesn't have nearly as much range and it's CC is weaker.
If you've ever seen a Draven come out of lane with 0 kills or maybe even only 1 kill, Ashe would have had a bigger gold bonus. Ashe does not need to get kills to get her extra gold - Draven does.
Her late game power is not as good as Jinx and Tristana if you're measuring power solely in terms of DPS. Ashe's ult goes a long way towards winning teamfights, and is excellent for forcing disadvantageous fights on the enemy team. Neither Trist nor Jinx are capable of doing so.
Where is she fine? She probably has one of the most powerful ultimates of all of the ADCs, and one of the most powerful ultimates in general. If you could take any other ADCs ultimate and replace it with Ashe's, you can damn well bet I would do it. If I could, I would replace Graves ult with Ashe ult, Jinx ult with Ashe ult, Trist ult with Ashe ult, Cait ult with Ashe ult, etc etc etc. If her team has an advantage, it is very hard for the enemy team to recover because Ashe is excellent at forcing disadvantageous fights and getting picks - NO other carry in the game matches Ashe for engage potential, and currently the only other champions with perma slows built in are Olaf and Nunu off the top of my head. Ranged perma slows are insanely powerful, and once a champion with a gap closer gets in your face, who would you rather be at the end of the day? Kog or Ashe? Hell, Ashe has better defense mechanisms than even Jinx does. Ashe has an on demand stun that stops gap closers - Jinx does not. Once gap closers are over, Ashe can create distance between her and her target with her slows, Jinx cannot.
Ashe is fine. If anything, give her a better passive, but that's it.