I understand what @splichois trying to point to and I also understand the difference between what @YeahTheProis defending here. Disregarding what is actually being talked about here, splichos combative reaction does suggest personal feelings towards you or your server.
Now to the topic being discussed. In the end, paying upfront or paying afterwards leads to the same conclusion. It is a motivating factor to many, especially to clans/alliances that are confident and big enough to win. In the end, you are rewarding the biggest/strongest clans for playing on your server and a parallel can be made to just straight up paying them. They simply risk more by being payed based on their performance afterwards and not initially upfront.
However, while the motivational factor does make a difference, it still does lead to the same conclusion. The best and biggest clans were previously getting payed proportionally based on their numbers and exposure they could bring with how many members they can round-up to win now.
Essentially, theoretically, respectfully... you are walking down on one of the 2 slightly different paths leading to the same destination, your path being easier to morally defend than the other.
On a personal note. I am more of a fan of this method, while I despise the upfront payment.