If you look at the 4 year cycle, you will be looking at the supply side, so you would be missing half of the equation and ignoring the reserves of bitcoin. So, yes the 4 year cycle is short of a self-fulfilled prophecy, but it would mean nothing if it were not for the traction that bitcoin is getting among a wider owner´s base than ever before, and for the investments that are being done through traditional funds and others.
So long story short there is a factual basis on this, sure it is still supply and demand and that is changed constantly as well and that is why we are not really worried that much about the supply and demand when there is a fall because we know that every fall is followed by an increase and every increase is followed by a fall.