Why do large images stored in database hurt performance
There's more to life than performance, like data integrity. If you only care about performance you should be writing all your code in Assembly. 

There is a higher risk of screwing things up by using the file system:

If you keep files in the file system, you now have two things to backup instead of one.

Other stuff: dealing with orphaned files. Dealing with file path security issues (path traversal). Preventing users from accidentally deleting files. You need to replicate your db security to the file system now. 

If you're dealing with pictures of cats, go ahead and use the file system. If you're dealing with x-rays, use the database.

If you're so concerned about performance, use the filesystem as a caching layer. Ex: GET /files/12234 -> if not on disk then fetch from db and put on disk -> read from disk.

Use incremental backup for your database.