Credit where it is due. For finding people it is excellent: filters by title, company, headcount, geography and recent activity, kept current by the people themselves. As a prospecting database it earns its price, and nothing here replaces that.
It cannot rank a connection by strength. A first-degree connection is a first-degree connection whether you speak weekly or accepted a request eight years ago. For deciding who to ask for a favour, that distinction is the entire question.
It only sees one person's network at a time. TeamLink widens it to colleagues who also have Sales Navigator seats, which in practice means the sales team. The relationship that opens your target account is usually held by an engineer, a customer success lead or a board member - none of whom have a seat.
It cannot see relationships that were never on LinkedIn. Two people who worked on the same team for four years and have exchanged email every month since may not be connected on LinkedIn at all. That is one of the strongest routes that exists, and it is invisible there.
Alongside, usually. Keep Sales Navigator for finding and researching people; add something that scores relationships across the whole company.
Pick an account you want and could not get into. In Sales Navigator, list everyone at your company connected to anyone there. Then ask yourself, for each one, whether that colleague would actually make the introduction if asked.
You will usually cross out most of the list, and you will do it from memory rather than from data. That gap - between connected and actually knows - is what these tools exist to close, and it is why a list of three hundred mutual connections has never produced a meeting.