It’s not different, but denying coverage for pre existing conditions is illegal in the US. Also, there is a limit to the ratio between the highest premium and lowest premium in the insurance pool, along with out of pocket maximums so you will still end up with the healthy subsidizing the unhealthy.

Incentives to make people healthier should not be a problem with these constraints (max premium rations and guaranteed coverage for everyone). It’s no different than offering a lower car insurance premium to someone that doesn’t drive drunk.