Not needed at all, an FC that nags you to go on discord is an FC not worth staying in. I use the game's FC chat and Linkshell chat all the time, and so does most of the community; it's only a small percent of people who refuse to use the game's chat system.

While voice chat is good when there's 2-5 people, when it gets into the higher numbers like 6-15 people it's actually a detriment to communication.