> Agile did it.

No, it didn't.

> Developers became resources to be pluged into existing projects sprints.

> Want it quickier just add more resources.

Except for the word “sprints” all of that long predates Agile. This common management attitude was the central target of The Mythical Man-Month, which was published 26 years before the Agile Manifesto.

Huh? How does that even work?

Usually adding one new resource subtracts a resource overall because they take other resources time. In the best case it may give you half a resource boost but it puts pressure on supporting units.

Especially if you only think of them as ‘units’ rather than individuals with strengths and weaknesses.

It doesn't.

Not if you want it doing on time, budget or to any degree of quality.

You get more bricks but a worse wall.