The interview consists of 4-5 panels of 2 interviewers. Each panel is generally 1 hour long.

I'm already out. The kafkaesque bureaucracy must be epic. I suspected it the moment I read "Mailgun team (level II or III)." This stratification metric means the owners lost control of the organization. When you no longer have the capability to assess and judge your individual employees (nor trust your management to judge) at any level, let's at least give them some increasingly narrow vector title so we know who is more competent than someone else in a pinch. Because our concern is not looking foolish, so we rely more on the people who get paid more in a vicious cycle of incompetence.