I don't mind Discord being a centralized platform for open source project discussion, if and only if the only roles it serves specifically play to its one strength, which is real time discussion. Asking for live support (from the dev if they are there, or the community if they are not) and doing live bug triage are the two big use cases.

Should contact for these things be real time? Maybe, maybe not. Async discussion like you get on forums or via email can do the job. But if you value real-time chat, Discord does it well.

Everything else? Do it elsewhere. Do not make Discord your only bug tracker. Do not make it your only wiki. Do not make it your only source of documentation. Do not make it the only place you broadcast updates or announcements. Do not make it your only distribution platform for critical downloads. And for the love of god please do not make it the only way to contact you. I don't care if you allow Discord to additionally do these things using integrations, that's fine, just stop trying to contort Discord into your only way of doing these.

Is Discord the only capable option for real time chat? No. But it has several things going in its favor, namely how one can reasonably expect a good sum of their target user base is already using it independently for other purposes, in addition to its numerous QoL features.

It can also better integrate into the dev's personal routine if they already use it independently. Like, do I have an email address? Yeah. Do I read my email on any reasonable interval? Hell no. My email inbox is little more than a dustbin for registration confirmations and online order receipts. I've had email for decades and I think I can count the number of non-work, non-business conversations I've held over it in that whole span of time on one hand. Meanwhile, I'm terminally online on Discord. So if I'm gonna be a small independent FOSS project developer, am I gonna want to interface with everyone over email? No. I'll still make it an option, because being only contactable on Discord is cringe, but it will not be fast. Discord will be my preferred channel.

Should I put more effort into being contactable on other platforms, because it's the right thing to do? Meh. I have no duty of stewardship to be available on platforms available to anyone in particular. I maintain this hypothetical project for free, on my own time, of my own volition, and I provide it to you entirely warranty-free. I have the courtesy to make all static resources available in sensible public places, and I provide email as a slow, async way to reach me. But if you want to converse with me directly in real time, you can come to me where I'm hanging out.