Unfortunately the single final exam selects for lucky people. Did you learn the right thing? Are you healthy and well rested on the day? Can you perform under arbitrarily selected stressful conditions? Are your executive functions fine with that plan?
The responsibility part is just one element influencing the result.
Your argument seems to imply that the only thing that an exam is possibly allowed to measure is ability to answer a question at some arbitrary point in time. It also separates the people with the wit to understand a bunch of topics in a span of 3 or 5 months, the ability to plan accordingly, enough self control, and some motivation to see the plan through from the ones that don't. That's not a bad thing, as diplomas are often used as a proxy not only for intelligence, but also for suitability to certain jobs.
Only if you were planning to scrape by. If you actually know the material (the thing the exam is supposed to determine), you should do fine, and any good or bad luck will tend to average out by the time you graduate. Besides, there really aren't any alternatives left. Completed homework had some weak-ish signal for a while, but now it doesn't.
What about frequent in-class proctored quizzes?
>single final exam selects for lucky people. Did you learn the right thing? Are you healthy and well rested on the day?
If it's a well-designed course it should be clear what the content of the exam will be. If not, it's the professor's fault. And barring rare emergencies being rested on the day is also generally a matter of preparation, not luck.
I liked my prof's approach to exams:
"You may bring one 8.5x11 double-sided cheat sheet into the exam. You may write anything you want on it. And I promise you that if you prepare such a sheet, you'll never even look at it during the exam."
And he was right.