[jltsiren]

My point was that if a paper needs 30 pages, don't submit it to a conference. That makes as little sense as submitting an algorithms paper to a zoology journal. Conferences are centered around talks, and you can't present a long paper adequately in a short talk.

Journals can be more flexible than conferences. They don't need page limits, because they don't have the physical constraints imposed by conference dates and the number of parallel tracks. But journals also have audiences, and audience expectations are more important than your paper. You should take those expectations into account when choosing the journal. Don't send an algorithms paper to a zoology journal, and don't send a long paper to a journal that focuses on short papers.

Write the paper first, and then choose a journal or a conference that publishes papers like that. Just as there is no single page limit that fits all papers, there is no single venue that publishes papers of all lengths.