Any hub actually worth using (Thunderbolt ports, high enough charging wattage, dual displays, 2.5Gb Ethernet) will run you like $300-$400, which is almost half the price of the Macbook. I'd rather have a couple more ports on the device.

But if the extra usb-c port is taken up by a charger what's the benefit?

Also the air physically can't accomodate USB-A, ethernet, hdmi etc.

You're not charging your laptop 100% of the time. The Air runs like 12 hours or more on a single charge. A Magsafe port is useless all that time.

Say you're at an airport, waiting for your flight, and wanted to charge your iPhone and Airpods at the same time.

The 35W power adapter (included on all non-base models or a $20 option otherwise) has 2 USB-C ports which should cover this use case.