I just don't see why having someone hard countering Tracer

I think the issue is that flankers are supposed to be the counter to snipers, not the other way around.

Tracer has counters. Reaper is a strong counter. She can do basically nothing against Pharah. Junkrat can make paths completely impassable to her, she's the most vulnerable hero in the game to his traps since you're frequently blinking into doorways without seeing them, and a single concussion mine usually spells doom. Even Symmetra is stronger against Tracer since her turrets slow her and a full nest kills her so fast. Soldier 76 can kill her very, very fast and is fairly hard for her to kill if he puts down his healing.

And McCree just annihilates Tracer. If she's close enough to fight him, he's close enough to stun, and if she's farther away, he has a hitscan gun that can kill her in moments while her gun does nothing.

Tracer has counters.

The question is what Tracer is supposed to counter herself.

The point of flankers is to distract and force teams to turn their attention and to hunt those at the periphery: healers and snipers.

The problem is that Tracer is supposed to counter Widow and right now Tracer is being countered by Widow.

truthfully maybe the Tracer is fucking up

I don't think this is really fair. There are places that Widow can get to that are literally unreachable by Tracer and there are plenty of places where there's no side path to a sniping perch that doesn't expose Tracer enough to offer Widow a chance at a kill (a chance that a decent Widow will take, since all they need is a single bodyshot).

And that's if the enemy team is relatively uncoordinated and not purposefully protecting their golden Widow. And even if you do get up near her, you can't generally catch her unawares because (a) wallhacks (b) the mine acts as an early warning system and (c) almost every good widow quickly scopes out between every shot since scoping in/out is so fast.

Put another way: look at pro games. Do you see how many of them are playing Tracer into Widow to be the counter flankers are supposed to be to snipers? Do you think that's because the pro Tracers are fucking up too much?