A first score of 38/76 as a Legend would result in a 76 average, This ain't unusual when stepping to the back tees for the first time with "Master" equipment! Guess what, one of my first Legend scores was a 79.
OTOH, players talk a lot of trash about unknown characteristics of the game which have become more obscure over time. When that chart was the only factor (before 2013!), you only needed some knowledge of non-linear algebra to get through. From then on, several new factors have been introduced which made it more and more impervious while the company would avoid clarifications.This includes factors which weaken the chart's requirements of RRs and average.
The hidden rules for mobile play which work w/o ranked rounds were the last blow. A completely new logic, and those who experience them are less present in the fori. Thus there's not much more than guessing.
Good for the company, as the unknowing player will better accept the heavy grinding necessary in the upper tiers. The chart above plus the XP reference tables are player efforts to pierce the curtain, but this only goes so far.