That is not my position. I have repeatedly stated that any decision by a Secretary of State would be subject to judicial review. It is not a legislative act, which is what a bill of attainder is.
It is a member of the executive of Colorado, the Secretary of State, making an initial determination of ballot eligibility, pursuant to the constitutional provision. When a constitutional issue is raised within the scope of the duties of an executive branch member, the supremacy clause requires them to consider the constitutional issue.
Government officials in the executive branch have to make initial assessments of their legal and constitutional obligations all the time. Those determinations are then subject to judicial review.