Strong internal linking can reduce the backlink burden, but it cannot replace external authority outright. Internal links channel the authority your site already holds toward a specific page, so a well-linked page on a trusted domain can rank with fewer external links than it would otherwise need. What internal links do not do is create new authority; they move existing authority around. So the honest answer sits between the poles: internal linking lowers how many backlinks a page needs, without making backlinks unnecessary for genuinely competitive terms. The pivot is that internal links channel existing authority but do not generate it.
The channeling effect is real and observable. When you link to a page from your strong, established pages, you pass it relevance and a share of the trust those pages have earned, and you make it easier for Google to find and value. On an authoritative site, that internal flow can be enough to carry a page into the rankings for moderate terms with little or no external linking, because the well it draws from is already deep. The page borrows authority the site has, rather than waiting to earn its own from scratch.
The limit is just as real. Internal links can only redistribute what the domain has earned, so on a young or thin site there is little authority to channel and internal linking alone will not carry much. And for competitive terms, where rivals have substantial external link profiles, internal flow rarely closes the gap by itself. External authority is what proves to Google that the wider web vouches for you, and no amount of internal routing manufactures that endorsement. Believing internal links replace backlinks over-claims; believing they do not help under-claims.
So use both deliberately. Build strong internal links to route your existing authority to the pages that need to rank, especially when your domain already has trust to spend, and let that reduce how many external links those pages require. Then keep earning relevant external links for your competitive targets, where channeled authority alone will not get you there. Internal links stretch your authority further; backlinks are still how you grow it.