As Lead Link, your first accountability is "Structuring the governance of the circle to enact its purpose and accountabilities".
If the governance proposal causes harm or moves the circle backward by decreasing the clarity of the governance of the circle, then your objection seems to be valid from your Lead Link role, as the proposal impacts directly your Lead Link accountability...
To answer your second question, article 3.2.2 of the constitution gives some clues (last paragraph): "Finally, a Proposal is always valid regardless of the preceding criteria if it is made solely to help evolve the Circle’s Governance to more clearly reflect activity that is already happening, or to trigger a new election for any Elected Role."
So, as proposal creating overlap in accountabilities between two roles decreases the clarity of the governance, this proposal may be constitutionally non valid...
Any other perspective?
Hope that helps!