Correct. However, using a huge premade deck is not a bad idea in the sense that it's a huge time saver.

For me, creating an anki card takes between 1-2 minutes, depending on how slow the dictionaries (plural) are. So, 30-60 words per minute (45 avg) means it would take me almost 4.5 hours to input a measly 200 words.

I can write down 200 new words from one episode of a tv show. You can see where this is going. For Korean, about 5-6k words are recommended to begin having non-basic discussions. 5k words at 45 words/hour is ~110 hours.

Instead, I suggest using a parent deck that has a premade deck + your personal deck as children. This lets you have the best of both systems. You can use the Hoochie Mama! plugin [0] to properly randomize your review queue for child decks. Anki by default pulls cards in order from child decks.

Note: All of this assumes that your pre-made deck is of good quality. I can't speak about other languages, but Evita's Korean deck (5.8k cards) is sorted by frequency. It's fairly good, at least until you get to more of a intermediate level.

[0]: https://ankiweb.net/shared/info/1460733408