You are using the exchange because of the premium cost. You could still buy coverage even with the preexisting conditions because they can’t offer policies that deny coverage.
I know because I just did it and have every year since barky care began.
I paid $21K in premiums in 2017. I’ve always paid my way and everyone else’s to boot.
I don’t know how you are buying insurance that covers pre-existing conditions outside of the exchange because I can not. The pre-existing law only covers policies offered by the exchange. If you have a pre-existing condition you might want to check your policy because it may not be covered. If you paid $21K for an independent policy you got screwed. An independent policy for me is a 1/3rd of what the exchange is but it will not cover my issues.