Rmcoo - all those tournaments which you have referenced make their seedings with respect to transparent and traceable set of criteria. And then adopt the standard or a variant on the 1v16, 2v15, 3v14, 4vs13 (etc.) bracketing.
On the specific question of whether slinging is OP as a strategy - that can only be answered with respect to an opponent's ability to implement, counter and execute the same strategy. Hence it is important to know when a ruthlessly efficient sling is being executed against a sub-par/equivalent strength opponent. Given that Legends are absolutely schooling Warlords to the point of competitive boredom - what are they doing there in the first place?
On the specific question of whether slinging is OP as a strategy - that can only be answered with respect to an opponent's ability to implement, counter and execute the same strategy. Hence it is important to know when a ruthlessly efficient sling is being executed against a sub-par/equivalent strength opponent. Given that Legends are absolutely schooling Warlords to the point of competitive boredom - what are they doing there in the first place?