A lot of that already exists on Titan Network: https://www.cohtitan.com/forum/
Quite possibly true, I don't spend a lot of time over at Titan (never really did), but then why have separate forums in the first place?
It seems to me that the Homecoming folks are doing things in such a manner as to create their own identity/space. As such, it seems that they might want to make it as complete as possible. Why should the players be sent off to 2 or 3 different forums to get the information they need to play Homecoming content?
Discord is, as has been said, good for smaller groups of people. However, it's very difficult to keep track of important info or questions with larger groups. Questions and information get lost, and because they get lost they are left unanswered or ignored.
Well organized forums have a sense of stability, and can help take the load off of Discord.
Agreed about well organized forums having a sense of stability and take a load off of Discord. As to why have different forums? Because, like it or not, there are multiple groups running CoH game servers already, not just Homecoming. There will be even more CoH game servers in the future. In the end, they're all City of Heroes. Instead of looking at one particular server's forum, there can be central forums that people can use to share information across servers.