You may be right concerning the TL threshold, Cerino, but I still can't see any justification in the numbers for a further separation.
The last stats by CS names 1078 TLs. Of these, 193 passed a 57.0 ave. and 320 have achieved 58.0 or better. The average average is 59.57.
Thus, separating the top players would create a meager pool of high class players, once they have fulfilled the extra rounds to tier up (>100 probably?).
What for? Would it be more fun for them? Is it necessary to keep them away from the second-best?