it is quite easy to advance from amateur to tour master. That is pretty straight forward and simple because you need so few rounds to do it. For example, you can go from Master to Tour Master with only 40 rounds at average of 63 or lower. The problem is once you hit legend it grinds to a complete halt as you all of a sudden need 500 rounds as a legend with an average less than 60. That's more rounds than you have to complete for all the other tiers to the point combined.
So going from amateur to legend takes less time than going from legend to tour legend.