I am an early-career researcher in mathematics. In general, after submitting a paper to a journal, it is advised to wait six months before requesting information about the status of the review process. In other words, in mathematics peer review takes a lot of time.
Having said that, I tend not to fully understand why a reviewer would take 3+ months before recommending to reject a paper. Certainly there are cases where this is inevitable (e.g., if the paper is highly technical), yet I would expect reviewers to keep a manuscript for more than 4-6 months only if they are willing to recommend acceptance.
So my question is. Is it ethical/generally accepted for a reviewer to recommend rejection after months from receiving the manuscript?