> I've always felt that if I can't get through an interview with a little prep and my existing skills, I don't belong.

I have this feeling too, but I am not sure if it is warranted.

Let's do a thought experiment: grab an engineer at random, don't tell the interviewers that they are already a colleague, and subject to the same interview process as everyone else. Now, is this engineer going to pass the interview? Maybe, but I would not be surprised if most failed.

It's very rare that the interview process will actually test anything that's used on the job.