The original recipe is, sure. But part of the fun of cocktails is experimenting with what tastes you prefer. The parent said they weren't enjoying what they ended up with, so I'm recommending tweaks. A little extra gin is a pretty standard way to make the campari more palatable, used in plenty of bars.

yes and the original manhattan recipe calls for equal parts vermouth and whiskey. you probably wouldn't want to drink it like that.

not only do people's tastes change over time, but so do the ingredients themselves. you can't necessarily buy the exact same gin, vermouth, and campari that was available to the count a hundred years ago. of the gins and vermouth available today, there is quite a range of diversity. you leave a lot on the table if you aren't willing to tweak ratios based on the ingredients you have.

Not a lot of bartenders would agree with you that 1:1:1 makes the best Negroni, even though it's the original recipe.