I’m a Bad Developer, That’s the Only Reasonable Explanation

Everyone else only has a very high-level concept of whether they think you've been doing what you're supposed to do. The optics on this must be controlled. You do not want to be one guy in the hierarchy away from getting shitcanned because everyone except your immediate boss thinks you don't finish enough tickets or whatever.

Look better than everyone else. Employment is a popularity contest. To succeed in a career, do your job well enough that you don't get into trouble, and spend the rest of your energy on social and optical development.

I must say, however, that "working overtime" (that is, sitting in your chair and looking fancy until 8pm at least 3 nights per week) is a near-necessity for someone looking to climb the ladder in most organizations. Since people don't know if you're doing a good job or not, the amount of time they see you in the office is a big component of their evaluation. They assume you are working if you are butt-in-chair. You need them to think you're a hard worker. You should never be the first one to leave unless you make sure everyone knows it's a special event for which you cleared PTO approval process, and you should be one of the last to leave at least 3/5 of the nights.

Sure it is. Impostor syndrome is defined as the state of affairs where your emotional assessment of your competence is lower than your actual competence. The definition does not depend on which aspect of the task is being discussed. "I can't write code" (when you can) and "I'm too slow" (when the people who appear faster, are doing it by just sweeping bugs under the carpet) are both impostor syndrome.

I will add that by the sound of things, the reason you have impostor syndrome is because your previous bosses have been bullies, sadists and sociopaths who successfully accomplished their goal of damaging your morale for their own pleasure. This is sadly not a rare state of affairs, but it's not universal either. Never be reluctant to look for another job if your boss is an asshole.

There are too many bugs in the code. Okay. Why? Well we don't have good testing set up. Why? Because time was not allotted for writing test code. Why? Because it was rushed. Conclusion: You either pay the cost up-front or after-the-fact. Either way. However if this is a constant thing then the real problem is: "You have too many features being built for the size of your team, either increase the size of the team, reduce features, or prepare for big problems."

From personal experience I can say me working at "optimal" power, that is optimal sleep, no external life problems, not sick, generally very happy is maybe 30%-40% more productive. That seems like a lot, but if you need 500% the productivity, you ain't gonna get it by making a person feel like junk, not get needed rest (vacation / day off), not letting then handle family issues, etc. I can get a developer working at 100% more productivity, but only for a short amount of time, then they burn out which requires EVEN MORE rest time.