I can agree with the majority of that. There is room for all shorts of different variants of tournament play. I think where we differ is I think such games should be one off games and not staple games.
There is also little to no disadvantage to the ones in the smaller leagues when facing a diamond player in that smaller league as stats and game play are different in each league. The player with the advantage in such a situation is the player who more routinely plays in that specific league. Moving down can be just as hard as moving up is. The only outlier I see is the Novice league which will have the newest of the new players learning the basics in which I believe would be a good idea to turn into the Learning League.