For me, it's easier to remember that aliases acts like a dictionary, so I can treat it like any other dictionary. With "unalias" I have to remember the command. As I rarely use unalias (a few times over a period of years), I typically have to search the web on how to remove an alias.
And if it really bothers you, I'm pretty sure it's trivial to define an unalias function in Xonsh that will act as you expect (without needing parentheses).
It's part of the beauty of Xonsh - many such commands you're used to can be brought into it by writing fairly simple Python code.
For me, it's easier to remember that aliases acts like a dictionary, so I can treat it like any other dictionary. With "unalias" I have to remember the command. As I rarely use unalias (a few times over a period of years), I typically have to search the web on how to remove an alias.
And if it really bothers you, I'm pretty sure it's trivial to define an unalias function in Xonsh that will act as you expect (without needing parentheses).
It's part of the beauty of Xonsh - many such commands you're used to can be brought into it by writing fairly simple Python code.