I've heard the metaphor that "writing your ledgers in pen instead of pencil doesn't make transactions irreversible" - meaning that in the same sense, actions on the blockchain could be coded to be irreversible.

The difference is in the authority of who gets to reverse transactions. For example, Tether can freeze and generally arbitrarily control USDT token. USDT therefore isn't really a cryptocurrency, since now a central authority can seize it. It seems to me that this authority undermines why one might want to use crypto in the first place. I don't think you can have it both ways.