A good Widowmaker on Shrine will die against a team of good everyone else
You're continually using skill as a way to try and shift the conversation of the viability of the character, when that's not really how it works. If you make suppositions like "if widowmaker player skill above a certain point and the enemy team is at or below that point or the players at or above that point are playing characters Widowmaker is strong against, then of course Widowmaker is OP HURR DURR"
We're not talking about that. We're talking about kit design, map design, overall meta (her winrate in competitive is bottom of the barrel). Skill is irrelevant; it's a team game, someone particularly good at something doesn't translate to how it interfaces with the other 11 players in the game so much as how that player is contributing to composition.
If your entire argument is that you get killstreaks with Widow, it's a really weak argument. The people you play against are shit. That is the far more likely scenario than that the general Overwatch community has no idea how to play Widowmaker effectively but you somehow do.
And for the record, Widowmaker is 4th place in KD despite her shitty winrate, so your citing of killstreaks isn't really contradicting anything; it's actually coinciding with the statistical trend that Widowmaker is good at killing people but not at winning the game.
Symmetra has the highest winrate in the entire roster, and Mei has a higher winrate than Junkrat. As for offense, Reaper has the highest winrate. McCree statistically fairs better then Pharah. Tracer fairs better than 76 (but they are both bottom of the barrel). You're right about Genji though; Shimada bro is dope.
http://masteroverwatch.com/heroes/pc/global/mode/ranked