Great question, and actually a pretty common objection! Here are my two cents:
You ask: "Would you validate my objection?" However, the Facilitator has no authority to validate or invalidate any objections (other than his or her own). The only circle member that has the authority to do that is the objector him/herself. What the Facilitator can do, is ask the objector some test questions to help him/her figure out whether the objection is valid or not. As far as I'm aware, there is only one situation in which the Facilitator does have the authority to declare an objection invalid, and that is when the objector is not willing or able to give an argument for one or more of the four validity criteria specified in article 3.2.4.
Here's the relevant bit from article 3.2.5 on testing objections: "The Facilitator may test the validity of a claimed Objection by asking the Objector questions. For a claimed Objection to survive the test, the Objector must be able to present a reasonable argument for why it meets each specific criteria required of an Objection. The Facilitator must discard an Objection if the Facilitator deems the Objector has failed to meet this threshold."
As long as the objector presents some reasonable argument for why the objection meets the criteria, then it's a valid objection, whether the Facilitator personally agrees with the arguments or not.
So really there's no way of knowing if an objection is valid or invalid without getting the specific arguments presented. The same objection could be either valid or invalid, depending on if and how the objector argues for it.
That said, I think you're objection would likely be valid, given the following arguments in response to the Facilitator's test questions:
1) Do you see a specific reason why this proposal would cause harm or move us backwards? --> Yes, this proposal would move us backwards, because right now this accountability exist in one place, and this proposal would cause an overlapping accountability to be added to a second, making it less clear who's accountable.
2) Would that issue be created by adopting this proposal, or is it already an issue, even if we don't adopt it? --> Without this proposal, there would be clarity about which role is accountable, so yes, it would be created specifically by the proposal to add this specific accountability.
3) Is that based on presently known data, or are you anticipating that it might happen? --> It's based on presently known data, namely the existing governance records (specifically the existing accountability) and this proposal to add an overlapping accountability. I'm not anticipating it might overlap and cause a decrease in clarity, I know it does interpreting the governance right now.
4) Does it limit one of your roles, or are you trying to help another role or the circle? --> In your case, coming from the Lead Link role, you can simply argue that it's coming from your role as Lead Link, looking at the clarity and coherence of the circle as a whole. That argument would not be valid coming from other roles, but they might be able to present a specific argument for why it decreases clarity for their role, if they're actually affected by this overlapping accountability (e.g. depend on it to get their own role's work done).
It's a long answer to a simple question, but I think the nuance here in judging or evaluating the validity of an objection is key, and it gets missed often. So I figured it was worth going on a little bit of a rant ;-)