Honestly, I learned 90% of the Japanese I know from conversation and I can tell you you need to know far less words than you would think to have a normal conversation about your day.
However, to have complicated discussions about politics, the book you read last week, a movie you think wasn’t so great, or your relationship, you might need more advanced vocabulary. But even then, you’re not going to use a word like “decorative lighting.” (You might use “atrocious” though, lol.)
For me, WaniKani is a foundation to help learn kanji I’m not exposed to during (written) conversations and to help cement kanji I already know/use occasionally. But I think using WaniKani solely for vocabulary can lead to issues since spoken Japanese is not the same as written Japanese, and it’s the same for English.
You have to supplement somewhere and fill in the gaps between conversational vocabulary you’ll use while speaking and academic vocabulary you’ll use while reading.

