Trying to turn on pro mini 5v with transistor

This is why I simply avoid mosfets, I don't think I understand them..

Eg, take a look at my circuit, why is the led not fully lit? Yup it's not saturated..is the simple answer buy a logic level mosfet? So how's it more of an advantage using a mosfet over a 2222?

That's where I'm confused...