Wait.. as opposed to now when the round robin winner has to win.. zero matches to be champion? And you're saying ONLY 1?
Not sure where you're going with this.
Are you talking about Asian/World League? That's completely different from the Gods Garden and Topanga A League. The former has players that are not Japanese, while the latter has only Japanese players. This means that the Asia/World League can only take place in 1 weekend so there is no time for anything more than 1 round robin.
Online Gods Garden1: ft10 single elimination
OGG2: ft3 round robin to qualify into the ft10 round robin,
Topanga A League 1: ft3 round robin, 1st place only has to win 1 long set to be champion.
Topanga A League 2-4: ft3 round robin, top players qualify to a long set round robin
Topanga Asia/World League: Long set round robin only
Topanga League has constantly changed their rules. In Topanga League they used to give an advantage based on who you beat in the ft3. The problem with that is that this doesn't guarantee 1st place of the ft3 round robin more of an advantage than anyone who placed below him. 2nd/3rd place could have more of an advantage depending on who he beat. Now 1st place of the ft3 round robin gets an auto advantage against anyone who finished below him.
The problem with the first Topanga League is that the original intention of the League was to utilize long sets to determine the absolute best player. 1st place having to win only once threw that out the window and gave way more importance to the ft3 as opposed to the long set.