Yes, having lived in Switzerland I experienced that, and it was the personal buy rather than having group plans was the feature missing from the ACA the most.
It isn’t really bargaining power of the pool, but the risk assessment of the pool you are in. Being in a hodge lodge personal pool means you are sharing risk with people who will have more expenses. That’s why Switzerland throws everyone into the same pool, so no crème low risk can be siphoned away.