Fabian,
Your numbers and calculations are almost certainly correct. Thank you for doing the leg work. But I think there is one discrepancy about the trip from Legend to Tour Legend.
I find it very doubtful that a new Legend will need to play 500 ranked rounds and have a sub 60 avg to reach tour legend.
I think a TM who reaches legend today will need 100 ranked rounds and a sub 60 avg. Not 500.
I'm just guessing here, but I think the reason everyone has to play 100 ranked rounds from X date, is more like a starter's pistol than anything else.
My theory is based on nothing more than what seems like it fits the existing mold:
20/ 70 avg
30/ 67 avg
40/ 63 avg
50/ 61 avg
100/ 60 avg
The jump from 50 games to 500 seems a bit much for hanging out at the penultimate tier.
Edit: Frankly, I think it should be 500 rounds and a sub 60 avg. The top tier should be next to impossible for normal people to reach, but exclusivity hasn't been WGT's m.o. in the past and I wouldn't expect that to change.
We won't know for sure until someone with fewer than 500 rounds, but more than 100 rounds since day X with a sub 60 avg reaches (or does not reach) Tour Legend.
As a side note, I hope that Tour Legend averages are true averages and not based on the best whatever number of games.