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In addition to permanent damage, which is what you are concerned about, incorrect behavior is also possible. One design I sort of inherited had a major ESD problem. It was long ago and I don't remember the exact details, but there was an input (maybe a reset input or an interrupt for a microprocessor) that was either floating or impropertly terminated. Developers with early access to prototypes reported that it would sometimes reboot when they set it on a carpet and walked around it.

This type of problem can be fixed with a strong pullup or a a few capacitors.

In my experience, the problems that you encounter with production designs in ESD testing (which may not be the same as ESD in the field) usually don't involve permanent damage to silicon. Usually it is incorrect behavior caused by a state transition on an input.

So ESD is not a myth. But maybe the problem is not what you imagine. Also, industry processes are in place to eliminate ESD damage. This includes ESD protection on individual parts and even individual transistors like your IRF510. So it may be that the reason you think it is a myth is because those processes and design details are effective at preventing permanent damage from ESD.