Isn't that effectively like saying "there's no fundamental difference between my three friends who like to talk about how democracy works and the Hong Kong government"?
The fundamental difference between Tether and HKD (or any other currency) is that Tether is not a legally recognized currency.
That may mean nothing to you, or to various other people who think that laws mean less than code, but it means a hell of a lot to most of the world.
This really is the root of all of this, and why we will really never be able to get through the lineup of sealions that will say "please explain to me..." every time you try.
The reasons something is a currency is because it is backed up by the power of the state. This includes (but is not limited to) the recognition of its status as legal tender within a the realm of a state, the ability to pay taxes in it, and also the very real guns and batons wielded by said state to enforce said authority.
There is no such thing as a currency that is not backed by some state, or at least some entity enjoying the broad authorities of a state. Tether (along with literally every single crypto product out there) does not.
But because primarily crypto was invented to snooker people who find the entire concept of state authority to be objectionable, this fact will never quite land.
The fundamental difference between Tether and HKD (or any other currency) is that Tether is not a legally recognized currency.
That may mean nothing to you, or to various other people who think that laws mean less than code, but it means a hell of a lot to most of the world.