I figured that some legendaries are more hard to get then others, for example, some types of loadstones are easier to catch then others – higher drop rate – which means that there’s no equilibrium between legendaries, so it’s unfair.
For example, I spend one hour trying to get charged loadstones, ending that time getting nothing. Otherwise when I go to Grenth event, I often get at least one corrupted loadstone. So you can see that the rate drop is really near to 0 when we talk about charged loadstones, different from the drop rate from corrupted loastone, what also makes them cheaper in Tranding Post (1g and 30s), and charged loadstone expensive (about 2g 50 silver).
Not forgeting to mention that everytime farm, I use full magic find equipment plus food and banner.