I really wonder, how is MAC so performance efficient, does not produces heat, has no fan noise and still has great battery life?

Even when they had intel processors, they were efficient. Is it because of the OS, or the hardware?

It's the hardware, Mac is/was also the best Windows machine and Linux machine so it's not necessarily the OS.

Generally speaking Apple focuses on providing a small product line with a lot more thought going into the design of each device, both internally and externally. With the iPhone and its ecosystem of profit streams they enjoy a lot more freedom to do this than other companies, having the iPhone absorb most of their CPU R&D cost instead of paying into Intel and AMD profit margins alone probably makes a huge impact on their BOM.

they do get warm. some programs such as Apple Compressor seem to cap GPU usage to 50% even when cold. but e.g. ffmpeg spikes up temp