Not worth the wasted time with the agent. Board as soon as you are allowed with your status, save a seat, and let your companion board at their assigned position.

Or board later at your assigned boarding position at the same time as your companion (if a flight isn't close to full..).

Or... if this is really that big of a deal. Contact customer service and get a written response and, assuming it is the response you are looking for, you can present to an agent if you have further situations like this. But that still holds the boarding line up...