Is it possible to play FFXIV if you don't use Discord?

[KageTokage]

I pretty much only use Discord because most groups attempting to get first clears of hard content demand it, not because I actually find it helpful.

I also have an easier time taking in directions via chat as opposed to having to listen to someone of potentially questionable sound quality.

[Sinte]

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.

That's a silly opinion to hold. Discord is not just a voice chat, its a community hub. If your FC has scheduled events, in and out of the game (for example we do hunts, mount farms, movie nights, savage raids, board game nights etc) it is simply impossible to keep all of that information together in-game. That's what discord is for. And no one is going to put a gun to your head and tell you to join voice chat on discord unless you want to. Most FCs that tell you to join discord, tell you that so you can see the text information on it and the events that are happening, as well as being able to be social with people in your FC outside of the game, for example via phone or laptop at work as many of us do.

But sure, if you're not interested in chatting with your FC members outside of the game and/or knowing when events take place, go ahead and not join, no one's going to "nag" you for it as you said (I imagine you think "nagging" is asking once or twice). But then why are you in that FC in the first place?

[Deceptus]

I do find it slightly irritating that lots of higher end content essentially requires a third party application in order to participate in it.

[SamSmoot]

I don't use it, but then, I do very little content that might require it.
I did when raiding in WoW, where voice was definitely necessary.