Can't fully agree in quite a few points. I understand how the author got that feeling tho. Doing interviews is always eating away at one's confidence, no matter who you are.
1. no one believes anyone can actually code - I experience quite the opposite. People expect others to be able to code just because they are currently employed as software developer. That's not true at all. Sooo many people can't.
2. Coding interviews are not about findign the solution but about showing some skills, showing how you handle things under pressure, your ability to explain what you do etc.
3. homework assignments are not done in professional environments.
4. interviews matter more to you: I agree and really hate this. You need to give 120% before you even get to the point where you can choose what you want. And at this point you suddenly have 90% of the power and often not enough energy anymore to make anything good out of it.
5. And yes it's even part of the job of the company to NOT let you know why you weren't hired. Still, I think you often know after the interview how it seemed. Good feeling = chance, no good feeling = no chance, weird feeling = usually weird job as well.
PS: One side note. A senior coding position might feel age discriminatory because senior is for talented ~28 year olds to mediocre ~40 year olds. A 50 year old should be architect/manager or not switch jobs.