Why do you say that the middle class disappears? They don't disappear; they become poor and then go into the poor category because they can't keep up with their current class due to high inflation and low wages. Also, maybe you are not aware of it, but even Bitcoin and cryptocurrencies are regulated and taxed in countries where they are legalized and bills are passed for them to be used by the general public, but they will be regulated, and people will be taxed based on their assets.
In the real world context, the poor have an high likelihood of becoming poorer but the middle class have every tendency of becoming rich if the effectively utilize the little they have. both the rich, the poor and the average individual get taxed but in the real sense, the rich even get to pay the highest amount in the for of tax. the only way most poor people get to pay their tax is usually in the form of VAT and nothing is usually deducted in form of income tax.
The rich has his worth visible to the public and hence, all tax laws can be implemented on him. the average guy can smartly play games around and grow his finance via small scale investment that are not al that visible which in most cases is not taxed. the major leverage that the rich have above the middle class is that with more resource, it becomes easy for them to invest not just into bitcoin but also into other profitable asset.