Nothing beats the waterfall for efficiency

Agile is not efficient. Not at all. If you want to be efficient there's nothing better than the good old waterfall. You define what the outcome should look like, you break it down into features and capabilities. And then you hand all of this over to developers to build it. There is no checkpoints, there is no discussions. All time available to the team is used building. This is efficient.

Agile it's all about taking one step at a time

Looking left and right and making sure you know what the next steps is before taking it. You check if the goal has changed, if you are still on the right path, and even how your team is doing. You heard this before it's about inspection an adaptation.

Track run vs Orientation Run

Imagine you are running track. You know exactly where you going. You can see the goal from the start. Hell, there is even lines on the floor to guide you. So, you give it all you got and just run. Efficient.

Now imagine an orientation run. You get map and a compass but you have to find the destination yourself. You don't know much about the territory. You don't know if there's any obstacles in the way, like a river you can't cross.

So you start running. But very often you put your head up and check if you're still running in the right direction and correct if necessary. This is obviously much slower and arguably less efficient. But when you don't know exactly what the goal and the path look like, this is the best way. This is agile.