Internal linking & site architecture — discovery + crawl-efficiency effects are SOLID; PageRank-flow magnitude is real but UNQUANTIFIED (Google publishes no weighting; survivorship bias plagues case studies)

Claim: Internal linking and site architecture have three separable effects, with very different evidence strength on each:

• Discovery (solid). Google discovers URLs by following links; pages with no internal links ("orphans") may never be found even if they're in a sitemap. Reducing click-depth from the homepage improves discovery and recrawl odds. Industry-consensus / Verified. Grade A/B.
• Crawl efficiency (solid for large sites). Clear architecture and shallow depth help Googlebot reach important pages — relevant mainly for large/complex sites. Verified. Grade A. Crawl budget is "over-rated" for small sites — see lifecycle Google explicitly tells sub-few-thousand-URL sites they DO NOT need to think about crawl budget — thresholds for caring are roughly 1M+ pages updated regularly, or 10k+ pages updated daily and Rule: crawl budget is not a concern for SMB-scale sites — sub-few-thousand URLs do not need to think about it, per Google.
• Importance / PageRank flow (real but unquantified). Internal links pass importance signals, and Gary Illyes has confirmed PageRank-type scoring remains in use inside Google's ranking systems. But Google publishes no formula or weighting, and the "dilution" logic is a framework, not a measured constant. Single-source / Directional-Speculative on magnitude. Grade C.

Case studies attributing ranking gains to internal-linking changes suffer from survivorship and selection bias: sites that rank well had many things right at once, so isolating internal linking's contribution is rarely valid.

Source: Google Search Central documentation; Gary Illyes on-record commentary; compass_artifact synthesis.

Confidence: Mixed by sub-claim, as graded above.

Caveat: Structured data does NOT substitute for HTML links — breadcrumb markup helps render breadcrumbs but does not pass link equity the way a real <a href> does. See Google hard gate — Google follows only <a> elements with an href attribute; onclick, <button>, javascript:void(0) navigation is not followed.