Widow’s effectiveness (and that of every one-shot/high burst based hero) is directly and indirectly tied to the impact that healing has on the game. Your problems will stay problems as long as:
Even outright removing Widow wouldn’t solve anything, you’ll just start complaining about the next best hero (or combination of heroes) that can burst you down fast enough.
For a more elaborate explanation:
Ironically enough most issues that come from Widow (and any one-shot based character by extension) come from the way that supports are designed in this game. Supports are incredibly heal-centric in this game. Now one-shots interact with healing in such a way (read: ignore healing completely), that they only benefit from having supports both on their AND on the enemy team.
Firstly Widow benefits A LOT more than most other dps from having supports on her team, because lack of self-sustainability is her major weakness and supports cover that without much effort (like, half of the supports can even heal their Widow from across the map to full in a matter of seconds). Without supports backing her up, a Widow just gets dove or flanked all the time and there’s not a whole lot she can do about it.
Secondly, Widow also benefits a lot from the enemy having supports, because it makes her way of dealing damage more impactful relatively. As I said, one-shots are the only form of damage that outright ignore any amount of healing, so the more healing that gets thrown around, the more efficient one shots become compared to other forms of damage.
So yeah, the effectiveness of one-shot based characters is directly and indirectly tied to the impact that healing has on the game. And removing one shots won’t help with this. Overall health pools are too low that people will just find a new way to one-shot (or at least pile up enough burst that it has the same effect as a one-shot in practice).