A widowmaker working on pure reflex can kill me before I’ve had a chance to comprehend what I’m looking at when I peek a corner.
Tracer can blink in, stick me, rewind, and I die and there’s absolutely nothing I can do except cross my fingers that she misses the stick.
Nobody has issues with either of these. In the first case, it takes practice. In the second…it really takes nothing more than luck to get the stick, but still nobody has a problem with it.
Scenario #1:
If I land a cross-court shot with dynamite and blow you up behind cover, not only did you ignore the dynamite callout (which is very, very loud) and not pay attention, you failed to notice the dynamite laying on the ground within 5 yards of you for upwards of three seconds.
It’s your fault for not noticing that I Kobe’d an awesome shot.
Scenario #2:
You dive behind cover at range and I use dynamite to flush you out even though I can’t see you.
Here I have to first land a slow, arcing projectile, I have to probably shoot it out of the air without doing an auto-shot (which is what I’m assuming you’re talking about) since if you see it you’re just going to run away and take zero damage.
Scenario #3:
You run around a corner to break LOS and try to get away, and I throw Dynamite to kill you without running around said corner.
If I were playing tracer, and just blinked around the corner and M1’d + melee’d you to death I’m going to guess that you would have zero problems with it even though because you’re running away it probably means you’re on low life anyway.
At the end of the day, getting hit by dynamite either requires you to sit there and pick your nose for the fuse timer and not notice the big, angry clump of dynamite, or it requires me to land a skill shot on something just shy of torb’s head in size.
To get maximum damage, which is what you’re complaining about, I have to land two consecutive skill shots in a row after avoiding d.va  and any shields your team has in place.
There are so many ways to wiff a shot with dynamite, you deserve the damage if it lands because it means you’re not paying attention to ashe, you’re not paying attention to what abilities she has available, you’re not paying attention to large, red, angry projectiles heading your way, you’re not respecting her effective ranges, you’re not respecting her defenses, and instead of working to get good you’re here QQing about her in the hopes that you can get her nerfed.
Get better at the game and accept that other heroes, that you don’t like, are also allowed to be good.