There’s 2 arguments to this, and they are at odds with each other.
Mechanically, spy does nothing that isn’t allowed, and it’s hard to argue that something that doesn’t break the rules as an addon should be removed.
Ethically, spy removes the skill component of detecting rogues from the combat log, and it’s prevalence compared to classic makes the rogue kit less powerful than intended. It’s difficult to argue that it should be left as is from this perspective.
I tend to agree with the ethical argument, myself. It operates within the rules but the information it provides frees up enough focus on the player to provide a significant advantage, and that unfairly impacts rogues. It cheapens the experience for everyone involved- rogues become less threatening, less powerful, and more manageable to counter.
As to the #nochanges wrinkle- yes, this did exist in classic. But as an addon the argument is more nuanced. Blizzard has an obligation to try and recreate vanilla as best they can for classic, but does this extend to making sure addons, an optional downloadable content, continue to function exactly as they did? An argument could be made that nochanges does not apply to addon functionality.