I'm not sure that this continues to be true, now that Git supports partial clones[1]. It's now a fully supported feature in Git to work with only a partial copy of the code and metadata. In my experience, this plus an fsmonitor[2] makes Git work fine on very, very large repos. This is how Microsoft scaled Git to work with their massive Windows monorepo[3]. (That particular article talks about the earlier work using Git VFS, but it eventually turned into these extensions that got upstreamed into Git, as documented in the Scalar repo[4].)
[1] https://github.blog/2020-12-21-get-up-to-speed-with-partial-...
[2] https://github.blog/2022-06-29-improve-git-monorepo-performa...
[3] https://arstechnica.com/information-technology/2017/02/micro...
[4] https://github.com/microsoft/scalar