Almost every writing system was imported from somewhere else, including something like half a dozen evolutions of the one we're using now (which was Latin, which was Greek, before that Phoenician, before that Egyptian).

What matters is that the Vietnamese use the script to write their own language, which is not the case for (say) romanized Chinese.

>early 17th century.

At what point does something become naturalized? This feels needlessly pedantic.

It's not a transliteration. What supposed writing system are Vietnamese originally writing in, before they transfer it to Latin script?

The Latin alphabet is not native to English, and it's a much worse fit for that language that it is for Vietnamese.

That is a really dumb point. Then Finnish has no writing system either, because it was created by a swede in the 16th century. Strange how there exist languages without writing systems, yet people write them?

it's the only official writing system that we have. The non latin scripts have practically disappeared from modern life.

We had centuries of Chinese scripts, which is definitely not native, then a short lived Chinese-like writing system that is the closest thing to "native", (it's not, see "Chinese-like"). Even that was not used as official system for as long as the current latin alphabet.