I'm not suggesting surrender, but I want to point out that a significant portion of the HN crowd seems to have a very specific perspective that doesn't align with reality. The average Discord user (hence, the largest percentage of the userbase) prioritize convenience, whether they're regular users or server creators. They don't care about being indexed by Google - they just want to connect quickly, chat, play games together, and so on.
This convenience-driven mindset extends to technical communities on Discord. Creating a server there is as simple as clicking a couple of buttons, whereas setting up a new forum requires significant technical effort and ongoing maintenance, besides $$$. These practical aspects are often overlooked in discussions, hence the failure of all these campaigns lead by a bit too technical people i.e. those who are willing to spend time researching alternatives and enduring their particular pains, and don't care about networking effects.
To challenge Discord effectively, create something equally convenient yet superior (like being indexable by Google). Wait for Discord's deep enshittification and seize the opportunity then. If it's not as convenient, don't expect users to switch. The average user won't invest time in learning new platforms when they can get everything faster and for free elsewhere.