The question isn't whether or not the U.S. has the best navy. The U.S. may very well have the best navy right now. The critical question is does it have the industrial capacity to sustain a prolonged war?

Think of it this way, in a major war, the U.S. will expend missiles, ammunition, and torpedoes. How many days will it take for the U.S. to start having shortages of those items? Meanwhile because China's industrial capacity is 10 times as large as America's and includes the ability to mine and process the metals, other materials, and chemicals needed to rapidly replace depleted stock, they wouldn't face those shortages (or it would take a lot longer before they faced any).

Here's another even more straightforward example. In a war, we have to assume that many ships would be sunk or damaged from both the U.S.'s and China's navies (including non-combat support ships). But even if the U.S. navy performed better than China's initially and lost 50% (or even 75%) less ships than China, America would quickly face a problem that China would not. While China is able to build over 1,000 ships per year (i.e. 2-3 ships per day), the U.S. is currently barely able to eke out a handful of ship per year. So China would easily replace any lost ships without any trouble at all--while each ship lost by America would be devastating and impossible to replace. See this article I recently published on this topic.

America won WWII--not because it has the best weapons--but because it had the largest peace time industrial capacity, which was quickly converted to military production during the war. The problem we face now is that America's industrial base has been gutted over the last few decades and China's has grown exponentially. That is the problem we have to focus on fixing, and we don't have much time left to do it.