My understanding is that katakana I used for tons of other uses like providing emphasis.

The reason borrowed words are written in katakana is too provide a clue that the word may have a non-standard pronunciation.

It functions similarly to how italicization does in English

Japanese, the language that has an entire sub-alphabet of broken Chinese letterforms dedicated to segregating native Japanese particles and inflections - lest they somehow taint the original kanbun.

Katakana are used for far more than loan words, loan words is just the first example you learn when you first start learning Japanese.

Among many other stylistic uses, katakana are often used for native onomatopoeia and are used to write native words all the time (usually in cases where the kanji is either not well-known or to give a different feeling to the sentence -- ズルい is a good example of this).

Latin fonts also have italic forms, sometimes materially different in shape from the straight forms.

This is largely similar.