On your second paragraph speak for yourself... I develop a factory shop control app mostly on a LAMP stack with ERP integration on an IBMi DB2. Believe me there are plenty of use cases for high DBMS and performance-driven apps in PHP.
As for the sentiment of your comment, yes there are many times isset and empty are useful, and understanding of how they are used is the only requirement for using them. They're my preferred way to test because I know what to expect.
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