Peaks interview questions

The interview was scheduled in three parts. The first part is an automated HackerRank. The first three questions are about LeetCode Medium level, and the last part is you coding a binary classification neural network with limited access to an LLM. The time limit is about 24 hours, and it took me about 6-7 hours in total. The second part is an introduction/cultural fit part, which generally went pleasantly. I asked them about the test, which seemed a bit too hard/FAANG-level. They explained that they don't have an HR team, and that they need to filter an enormous amount of candidates before they can proceed. Then, I was given a take-home assignment, the essence of which was to produce a report for advertisement expenses, and to do some predictive modelling for it. There were specific individually challenging parts of the assignment, and the scope for the tasks was quite broad. I managed to finish it in a day of full concentrated effort. Despite that, I got a generic, zero-information rejection letter. Given the substantial difficulty of the initial assessment and the amount of time and brainstorming the take home took, giving a bland and generic one-liner rejection letter strikes me as disrespectful. I understand not giving feedback on the initial stages of the process due to not having an HR team, but this stops being a valid reason by the time a candidate has spent substantial amounts of time and effort on a non-trivial take-home task. EDIT: I was later reached out by phone and was given an explanation as to why a rejection happened. I was due to some internal processes and decision-making that I'd rather not mention, though in general they were satisfied with the quality of my take-home. The one-liner is just their ATS system not being configured properly. Oh well.