Thank you for the clarification. I tried fc_disable=1, and I am not seeing it listed as disabled under Tools in the GUI. Am I to assume that is is, though? Runner says it's already disabled because I have QoS on. I liked knowing that HW Acceleration was off on my old router, the AC86U does not give me that assurance or a simple way to turn it off.
It's possible that some part of the closed source code will automatically re-enable it if it doesn't detect any incompatible setting being enabled. In that case, nothing you can do about it.