What needs to be done with Sivir?

Sivir is an extremely old champion in League of Legends. Sivir used to be a key piece to many team comps in Season 3.4. and 5. Now it seems as if Sivir is only pickable in extremely selective compositions. If the enemy picks Twitch, Draven, Vayne, Xayah,and Lucian it seems to be more than just a "rough matchup." Against the majority of adcs, Sivir can't really spell shield anything significant. Perhaps an Ashe arrow, or Draven E, but she simply doesn't win the trades. Many adcs have their power spike at around 2 or 3 items, Sivir's doesn't seem to really appear until she has 4 or 5. And even when she spikes the majority of adcs still out-damage her. Unless their entire team is tanky, why pick Sivir? And wouldn't you just go Vayne instead? You can win your lane, you can give it your all, but it has become clear that Sivir is outclassed not in player ability, simply in game mechanics. You can respond and tell me I'm wrong, but go ahead and tell me what you think. I think Sivir has a strong kit for past seasons, but with the additions of new champions, and changes Sivir doesn't seem to be involved. People love playing Sivir. They spend hours practicing their champion. This game that's all about champion balance, seems to make certain champions unplayable. Why is this? Please do respond, I'm curious about people's opinions on this matter. Thanks, LeBlanc Prince