Well, there is also the widespread belief that "if MySQL doesn't do it, it's impossible for any RDBMS to". When people say "scalability" or "sharding" for instance, this is what they're complaining about.
How about "if MySQL doesn't do it, then much more expensive databases might do it poorly after a whole bunch of effort"
I regularly work on DBs of 10s of teras with NO sharding or any of that nonsense.