Not true.

Different regions may receive different firmware versions, and network operators also frequently provide "customised" firmware that can affect functionality.

Phones can also vary very greatly depending on which suppliers are used for components, which factories manufacture them, and what kind of production processes are being used.

Even a single model may have literally dozens of variants with slightly different qualities in terms of stability and reliability.

And even with a single variant you are going to see a certain percentage of models with physical faults coming out of the factory. There is no way to avoid this.