Dilution begins not at a fixed number of links but at the point where each new link stops adding a relevant connection and starts subdividing a finite pool of attention.
The mechanism is closer to division than addition. Picture the value a page can pass to others as a quantity that gets shared across its outbound internal links. When a page links to four genuinely related pages, each link carries a meaningful share. When that same page links to forty, the share each one carries drops, and the links that actually matter now compete with thirty-six that do not. The page has not gained reach, it has thinned the signal flowing through every link on it.
The located point, then, is wherever the next link fails two tests at once: it points to a page only loosely related to the current one, and adding it pulls share away from links that genuinely deserve it. A link to a tightly related page can still earn its share even on a fairly link-dense page, because it adds real connection. A link added to hit a quota dilutes, because it takes without giving.
This is why the ceiling is a ratio, not a count. A 4,000-word resource that genuinely connects to fifteen related pages is not over-linked, because each of those fifteen links adds a real path. A 700-word post carrying fifteen links almost certainly is, because the content cannot support that many genuine connections and the surplus is just splitting the pool.
Looking at a link-heavy page, the question to ask is not “how many links is too many” but “does each link still point somewhere a reader here would genuinely go, and does the page have enough substance to justify them all?” When the answer turns to no, you have found the point where connection gives way to clutter, and the fix is to cut the links that were taking a share without adding a path.