1. People spend money to get stronger, A LOT of money. And the easiest way to make them feel stronger is to let them beat almost everyone who spend less than them. If that mode actually a thing then everyone can just rush to 85, save for ninjas and don't even care about half the game functions because they don't need power. Not even care about initiative because what the point to trying so hard to beat everyone else around you just to be place into a group where your effort & money worth nothing? That mode you suggested serve no purpose whatsoever.

2. Rewards for this mode are just too big, do you know why sage world battlefield give best reward? It's to encourage people spending and become one of the strongest, no point give even more rewards into a mode where 90% participate players don't even spend a dime.

3. If you want to fight people across many servers then space-time is what you looking for.

4. In the mother version of the game there is another mode where people climb tower and battle, however power still play big part, as it should be.

5. Also there will be a special sage world with arena rules however with different rewards that already happened in the mother version of this game (CN).

So yeah, no point add your suggested mode on top of everything.