Having finally seen what Discord is actually like for myself, this is what I can say about it now:
Discord (like Paint, Social Cu.be, Social Neko, and 3DSPlaza) is a cool website, with lots of wonderful people on it, and many different servers devoted to all manner of interesting subjects, such as gaming, anime, art, and many more.
All that being said, as cool as Discord is, much of what is done on Discord (such as sending public messages in different shoutboxes channels, and sending DMs to specific individuals) is also able to be done right here on Paint, and there are many features that Paint and Social Cu.be have that Discord doesn't.
By no means is this intended as a criticism of Discord (although it is certainly rather laggy and glitchy on the older devices that can actually run it, like this tablet), but rather as an acknowledgement that Paint and Social Cu.be aren't inferior to Discord or anything, nor are they inferior to any other mainstream social media websites, and that (unlike most of those other websites) Paint and Social Cu.be work well in almost all devices' web browsers, they don't collect your personal information or "metadata" to sell to advertisers and/or the government, they don't censor people based on their political views, and aside from just talking to other people (which can be done almost anywhere), they allow people like myself and countless others to engage in a variety of creative hobbies, such as writing blogs, drawing pictures, and coding.
The #1 reason why I use Paint (and Social Cu.be) WAY more than I use Discord isn't actually nostalgia or sentimentality, it is ease of use.
Using this old Android 5.1 tablet of mine, Discord is REALLY laggy and glitchy for me, and aside from that, there are a number of things on Discord that (especially when combined with the aforementioned lag) just make it incredibly awkward for me to do the simplest of things, such as to reply to a message without pinging the individual whom I am replying to.
I understand that Discord has lots of other features (such as voice chat) that I'm sure many people enjoy using, but for me personally, things like being able to customize everything with CSS and being able to write WAY longer DMs and blogs and such are far more enjoyable features for me to have than anything Discord has to offer at the cost of glitchiness and lag (and money that I don't have), and aside from the difficulty in me using them that is the other major reason why I prefer sites like Paint and Social Cu.be over Discord and Twitter.
(Almost every criticism that I have of Discord here can be applied to Twitter as well, although it is somewhat less laggy than Discord most of the time.)