You’re assuming Bap doesn’t just jump to high ground, which prevents Tracer from even reaching him in the first place (or take far more time.)
Not to mention, Bap will constantly be repositioning, which takes Tracer far longer than the 12 seconds to reach him. By the time she does, all of his CDs will pretty much be ready again.
And you’re also assuming that Baptiste doesn’t get any support from his team, which may not be the case if he’s playing close to his second support.
Even if she does get through all 3 hurdles (which isn’t exactly easy)… Recall CD (which is the one that matters) is 12 seconds, while Baptiste’s CD is 13 seconds. So Tracer has 1 second over Baptiste?
The point is, you’re not killing similarly skilled supports in OW2 unless they’ve wasted utility. That’s a large part of supporting: choosing when to use utility to survive or carry the team.