I have to say the "GOF" book was giant fraud, or at least a big mistake. It has no clear rules on when to use what pattern over another. This resulted in ambitious but naive programmers throwing design patterns at everything in ways that appeared haphazard to those not owning the coder's mind, creating "spaghetti objects". I went round and round in online forums trying to clarify the "rules" for pattern selection. It never resulted in anything definitive or fruitful. It's horrifically vague. The "art" had a cult-like quality to it.

Pretty much.

There are only five patterns that matter in real world software development.

Observable

Singleton

Composition

MVC

Inversion of Control

And the last one isn't even covered by GOF. The book is an out of date relic of 90s programming. Let it die already.

Being a best-seller does not make it fundamental.

If anything, that suggests to me that it is not. "Philosophy for Dummies" far outsells Plato.