Someone commented that the TGR novel mentioned (and this is what I'm not sure if it's true or not) that to get to the highest cultivation level possible in this world, it would take Xiao Yan more time to get to that level than it would take Lin Dong. I think probably 10 years more. But in the end, and this one I know happens, they both managed to get to that level at the same time. And this is why Mu Chen respects them a lot since they were from the lower worlds and yet they managed to become the strongest.