There's generally two ways to look at the relationship between USD and btc. The first is that bitcoin has intrinsic value indpendent of USD, so if the USD falls, btc (while indpendently stable) will "appreciate" in value relative to the USD. An offshoot of this is that the failing dollar would send people piling into btc, which would push the price up. The opposite of this view is that it's excessive wealth created by the stable value of the USD that creates the wealth necessary to allow people to speculate on bitcoin, and if the world's most stable currency failed, people would flee the riskiest assets in a massive flight to safety, which would tank the bitcoin price.
Personally, I fall into this second group. The failure of the dollar would tank the world economy, bitcoin included, which is the king of speculative assets. People will flee speculative assets and pile into traditionally safe assets, which would include gold, silver, and probably the Euro and Yen as the remaining stable fiat currencies.
You forget a few important things in your speech
More specifically, that Bitcoin is not valued just in the US dollars. It could indeed be priced mostly in dollars but the dollar just happens to be there, happens to be a universal yardstick. But if people start, for example, weighing gold in grams instead of ounces, gold won't lose value just because of that. That basically means that people which buy and sell bitcoins don't care much if Bitcoin price is denominated in dollars. They have their own currencies which are more important to them (including those you enumerated), and the dollar as such is pretty insignificant to these folks. So if there are more people involved in Bitcoin which are using these other currencies for their everyday activities, the failure of the dollar would mean nothing to them, nothing negative. To them, Bitcoin will be a separate currency in no way linked to the US dollar or the US economy unlike the stocks of the American companies. This is where you make a mistake by implicitly linking Bitcoin to Murika
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In short, Bitcoin is not some overpriced American stock
Stock has nothing to do with it, but it is overpriced in the sense that its value far outweighs its utility. But that's a separate point.
Bitcoin is denominated in dollars as well as other currencies, but if you're trying to sell the idea that the loss of the world's most stable currency from the market would mean "nothing negative" for the traders in every other currency, well that's a terrible position you've backed yourself into defending! Especially considering that it's the excess wealth created by our currently stable world economy that gives speculative assets their value. Guess what happens if everything goes to chaos... speculative assets crash. That's what the Great Depression and the Great Recession showed, as well as the Dotcom crash. All of it was speculation driven nonsense, and when the mania couldn't sustain the overpriced assets anymore, all that money that was propping up the speculative assets fled to safer assets. But I'm sure Bitcoin is the one speculative exception that would continue to thrive when a bulk of the buying pressure propping it up disappears, right? That's what you have to believe to argue from your side of it.
