Does Discord have some inherent advantage over conventional forums? I don't have much experience with Discord, so I'm curious as to why so many people migrate over to it (over regular forums).
From my own experience it is more like the old messenger chat, so a lot more live action of a discussion/group chat. Forum boards i'd say have better systems for lengthy posts and proper threads (although you can pin posts in discord which lets you jump to them.) Discord works a lot better for playing rpgs if you are able to get a handle on the coding, have the option for video and audio chat, and generally are a lot easier to upload pictures to.
I used Discord video chat to keep my RPG going through the Covid times. Now that we don't have to social distance, we sometimes still use Discord because I live an hour away from a lot of my friends.
Discord is great for real time or short-term open conversations about various topics, but forums like this one are better if you want to have an enduring reference.
Given the nature of tabletop miniatures wargames, any game system any army is going to want to galleries of completed models and terrain. They are going to want to have how-to guides for painting and modeling.
They are probably going to want to have army building guidelines, tier rankings for unit choices, battle reports, and tacticas.
All of these things are in my opinion easier with a forum system like this than they are on Discord.
I do think one of the aspects of Discord that make it popular is that that is cross-compatible. Discord has its finger in so many pies hypothetically a person with diverse and multiple interests could be part of a knitting Discord, a current events discussion Discord, a fantasy sports league Discord, and an RPG Discord.
I myself am part of the World Anvil Discord (which is very broad with many specific sub-Discord), my local gaming store (which includes tabletop miniatures AND RPGS), and Midjourney's AI art generator tool works primarily through it's own Discord channel. And it duplicates as an option to text friends through.
And it's free.