There's no scalar measurement for stability, quality, or strength so there's no direct comparison to be made. It's comparing vectors and the properties of each vector may or may not be things you care about but leaving them unspecified and claiming they're collectively inferior or less meaningful than other things is the straw man you're defeating. People have faith in governments for various reasons, giving their currencies value. People have faith in crypto for various reasons, giving their currencies value.

Nobody is making a claim of general superiority except you. The guy you're responding to simply says THEY have more faith in one particular currency. Why is that so hard to believe? They may not be a US citizen! It's not an objective statement they're making about the quality of USD, but a personal one. The straw man you're attacking seems to be a reflection of your own general idea that USD is the 'supreme' currency and anything having comparable properties in any way is some foundational challenge to this multi-faceted strict dominance. The impure and complicated truth is that each currency has strengths and weaknesses. It is a fact that for any given application and person any given currency can be better/worse for their application. If you exist exclusively in the United States and never break any laws, I can see why this might be difficult to imagine.

For example, some people place great value on being able to transact without the enforcement of American cultural values. This quality of the currency for many is objectively a negative property. Since all currency are largely valued based on fiat anyway these days, why is it so hard to imagine people having preferences more closely aligned with groups other than one of the most geriatric and monochromatic governments on earth?