A hub page is valuable when it adds organizing value, and thin when it is a bare link dump with no original value. The line is not the link-heavy format itself. Plenty of strong pages exist mainly to point elsewhere. The line is whether the page does work that the destination pages cannot do for themselves: curation, context, structure, and a navigational service users actually want. Where that work is present, the hub earns its place. Where it is absent, the hub is just a list.
A valuable hub organizes a topic so that a reader understands the landscape faster than they would by hunting page to page. It curates, choosing what belongs and what does not rather than listing everything. It adds context, short descriptions, and reasons each linked resource matters and to whom. It often provides a useful overview that stands on its own, so the page answers “what is the shape of this topic and where do I go next” before the reader ever clicks. That orientation is the original value, something the individual destinations, focused on their own narrow topics, do not supply.
A thin hub strips all of that away and leaves only links. A bare list of titles or anchors with no curation logic, no descriptions, no overview, and no evident reason for the grouping offers nothing the reader could not get from a search result page. It has no information gain over the pages it points to, so there is no reason for it to rank or for a user to value it. The format is identical to the valuable hub, the difference is entirely in the organizing work layered on top.
So when you build or audit a hub, judge it by the value above the links. Ask whether someone landing on the page learns the structure of the topic, gets help choosing where to go, and finds context they would not get from the raw links alone. If yes, the hub is doing its job. If the page is only a stack of links, add the curation, descriptions, and overview that turn a list into a service, or it stays thin.