The way I'm understanding it is that the current, pre-update Diamond 1 rewards are the equivalent to 10x, so after the update, if you're Diamond 1 and earning 2x rewards, you're actually incurring an 80% nerf to what you'd be earning now pre-update.
As far as which is better, you could look at Chest EVs by league and math out an 80% penalty to Diamond 1 and then compare that to the EV for Silver 1.