So, something that often gets brought up when discussing the balance of certain heroes (McCree, Doom, and Hog are the most egregious), is that while they have one-shot combos, Widow can one-shot anyone from any range every 1.5 seconds.
This… is a dumb comparison.
For one, Hook/Doom Combo/Doom Punch/Flashbang literally hand you the kill on a platter. There’s very little aiming that needs to be done for either of these four one-shot combos (outside of hook, but hook is also full of buggy jank that makes it hit more often than it should). On the other hand, Widow has to hit a headshot on an erratically moving target with no movement acceleration without any outside assistance unless she’s lucky enough to notice a stunned/CC’d target while charged up.
Secondly, Doom/McCree/Hog all have defensive capabilities as well as already good kits in addition to their one-shot combos. Widowmaker has a crappy Soldier: 76 knockoff, a buggy hook, and… venom mine (yay?). Compared to Air Roll and 3-tap primary, or Take a Breather, or Rocket Punch jumps, Widow’s defensive capabilities crumples (especially when you consider that her HEALTH was nerfed to 175, making her even weaker to dive)
Lastly of course, they all have real ultimates compared to Infrasight. Unless you are on a GM team with full comms, Infrasight is legitimately just making it slightly easier to get headshots, while Deadeye (arguably the weakest ultimate out of the three) can usually secure a pick on at least one enemy hero. Meteor Strike is garbage but at least does something (repositions and maybe gets a pick on a slow moving character like Ana), and Whole Hog can win teamfights if used creatively.
Anyone who thinks Flashfan/Hook/Doom Combo are balanced in COMPARISON to Widowmaker’s sniping is incredibly deluded. Widowmaker has no real kit other than her potential infinite range headshots. The rest of these characters have full fledged and good kits in addition to their much easier to land one-shots. If anything, this comparison is better suited to Hanzo, who can just one-shot by randomly spamming a choke and has better escapes against Dive than Widow.
TL:DR
Claiming that Flashfan/Doom Combo/Hook Combo are balanced by citing Widowmaker is dumb because headshots actually take a modicum of skill.