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

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.

The flight controller can easily handle minor manufacturing differences between motors. In fact they can handle completely different motors or propellers by reducing the power to match the least powerful corner. Similarly they can allow for an unbalanced centre of gravity simply by increasing power in one direction. Obviously it's better to keep things balanced, so all motors can operate at full power - particularly on a brushed drone that doesn't have much power to spare.

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