

I wouldn’t say you rarely encounter written hiragana. It’s in practically every sentence because, as you mentioned, it carries the grammar of a sentence. Particles, conjugations, auxiliary verbs are all written with hiragana.
As one of my Chinese friends in grad school put it: he could kind of understand written Japanese but had no idea what was going on with “those weird characters everywhere.”
This is exactly what my friend would say! Wikipedia is a genius example to use. That upper section is mostly nouns, not complete sentences, so it’s just kanji that are mostly readable to people to understand Traditional Chinese characters. The の character is a grammatical particle (written in hiragana) indicating that 最大 is modifying 都市, to give largest city.
And then all the “curvy” characters in the body of the text are the hiragana carrying the grammar of the sentence. You can understand the nouns and verbs since they’re written in kanji, but the grammar surrounding them is in hiragana. That’s why I thought it was odd for the other person to say you rarely encounter written hiragana. You really can’t write a complete sentence or much more than a single word without it.