Since my discord activity is growing by the month, is search good/great with (very) old content?
It's not perfect though. There's no exclusion filter option, some queries are automatically broadened without a way to enforce strict string matching (eg: searching enemies will also include results for enemy but wrapping in double quotes like "enemies" doesn't prevent this), the pagination when there are too many results for a query maxes out at ~200 pages even if more pages are shown/should be accessible via the navigation (seems like a bug), the pagination is also only at the bottom which adds a little extra time navigating and attachment filenames can't be searched.
That said, even with the above caveats I manage to find what I'm after reasonably quickly the vast majority of the time, even things years old.
But the search will let you specify time periods, channels, who sent the message, etc. It also gives a line of context around the result, which takes up some space, but I find is quite useful for, well, getting the context of the statement and figuring out what it meant.
I think the most important facet for (very) old content searching, though, is that you can almost immediately go back in the chat history to any result. Whereas other chat apps make that slow or difficult.
Just on this, most Discord mentions I've come across on HN describe how the user experience is what separates it from the competition and I'd agree.
The networking effect across communities doesn't seem anywhere near as strong as traditional social media where one might argue it's what keeps users retained. Few I've observed in the years I've been on Discord seem to care or recognize who someone is across 'servers' (Discord meaning), which is made less obvious by the encouraged feature of changing handles/avatars across communities to maintain quasi-distinct identities (even across related gaming chat). It's also not uncommon for some users block all PMs and friend requests from communities merely due to spam issues.
The communities using it that I've experienced are often doing so since it's the most convenient service for their purposes. Users can join with invites without signing up (a la IRC, traditionally), supports inline attachments (acting as an all-in-one image/video/file host), includes persistent, easily searchable message logs and just as importantly is all free.
A decent number of the communities I've encountered (ranging from software, subreddit/forum chat, game modding, media creation) could migrate elsewhere if there was an alternative suitable for their own needs. A number of them have migrated from other platforms before and one of the gaming-related ones even discussed potential future alternatives. If anything the self-hosted aspect would be the main drawback to a Discord-equivalent alternative (ie: the costs, maintenance).