It doesn't mean you will earn half, your multiplier will be 5x not 10x.
If everyone's multiplier is less than you can expect more SPS in chests, so you may actually earn more in $ terms. You can also earn more with rentals.
There are a lot of accounts whos multiplier will go from 10x to 1x. All those rewards going to them will be shared out amount those with SPS now.
RE: SPS Staking Multiplier for Ranked Battle Rewards