Some other advantages:
The kernel has a global view of what is going on with all the different applications running on the system, whereas your application only knows about itself.
The cache can be shared amongst different applications.
You can restart applications and the cache will stay warm.
Another big disadvantage is that the page cache is only useful for caching data of actual files and nothing else.
In the context of this article, many databases use the page cache to cache their data-structures, either in combination with private pages (ie postgres) or entirely (ie LMDB).
Some applications do use the page cache for non-caching purposes though, for instance IPC, or ensuring their working-data will survive an application restart. The memory is still associated with files naturally, but this is often regarded as a feature, not a problem. Some applications use files on tmpfs so that their page cache data is backed by swap (or nothing), the same as anonymous pages.