No, that IS the point. It's the entire point.

No, it's not. If the UK decides to reduce their Navy by the same proportion as the U.S. did, that doesn't decide for us how we are going to handle our relationship with them. That's still entirely our call, our decision. The entire US-UK relationship is not reducible to simply the size of the UK Navy, or whether they choose to downsize their Navy in the same proportion as we do.

You might believe that the only single thing that matters in determining what an alliance involves is the size of the other country's Navy, as opposed to cooperation and support on any of an infinite number of economic, diplomatic, regulatory, financial, institutional, or host of other interactions between those two nations. But that doesn't make it true. The decision of the UK to cut their Navy in half over the same time period that the US cut our Navy in half is not "the entire point" of the UK - US alliance.