As you guess, motors are approximately equal but are never balanced exactly enough to fly without active stabilising.

The receiver just sends the model the position of the sticks on the transmitter, it doesn't know anything about flying the drone.

You need a flight controller - a microprocessor with accelerometers that detects the angle and rotation of the drone and calculates the power required for each motor in order to match the commands from the receiver.

If you want a small brushed drone, you might as well just get something like this, as it's often cheaper than buying the parts individually:
https://uk.banggood.com/Eachine-E010-Mini-2_4G-4CH-6-Axis-Headless-Mode-RC-Drone-Quadcopter-RTF-p-1066972.html