In my experience, SQLite explain plans are by far the most useless of any database out there. No concept of costing, no buffer information, no explain analyze. It's almost like they don't want you looking at it.
A couple of obvious ones would be running as a standalone service, and supporting multiple concurrent writes. Both of these help support transparent handling of multiple concurrent clients, which seems like table stakes for a "real database".
...performance-wise. Not in general. It obviously does more than just opening a file.
Also, you don't get to choose your competitors. SQLite is single-writer focused and an embedded library, but it's a sophisticated database engine after all, so comparisons with other "real databases" are more than appropriate. This meme really needs to die. Even more so when all you're comparing is query plan debugging output where there is no justification for unreadable output.