yes, you can make constant earning through bitcoin trading. you must aware of daily updates and current market trend of bitcoin.
With bitcoin trade it is not easy to get a monthly fixed income. You may lose money due to factors that are not in your control. Especially if you are doing margin trade, you have to be very careful. It is possible to lose everything in your hand.
That's right its impossible to expect a fixed ans stable income from trading as it will be always changing depending on the profit and loss that you make and even if you are into majority times still you cannot come to a fixed income as your profits will be volatile depending on your capital.
People with large capital earn more. As you said, it does not make sense to expect a steady income from trading. The trade nature has variable parameters.
But I think it is more advantageous than fixed income jobs. A good trade will make a good profit.