Absolutely false.
SQL Server is capable of handling terabyte-sized databases with hundreds or thousands of users. It is cost-effective and requires minimal administrative overhead.
Please don't make statements about technologies in which you do not have experience.
MySQL requires considerable administrative overhead, similar to Oracle, though both are capable of handling large multi-user applications as well. MySQL is free, but lacks the features of more advanced database servers such as Oracle and SQL Server. MySQL is satisfactory for simple database designs.