Set text size as preferred, underline links (or not), turn off display name styles (or not), ui density compact or default, chat message display to compact, space between message groups 0px, turn off all the animated emojis and gif animation stuff if you want.
In client use, there's a button to hide member list (or not).
You can definitely make discord look like a slightly less dense IRC client (mainly because of the channel picker) if you want. And if you want to go really crazy use it in a browser and userscript customize it or use betterdiscord.
I think a lot of the features like embeds and emoji reactions add a lot of value compared to IRC (which I think is also why the IRC world is trying to add those features).
Personally I'd love to find a decent online community these days, my social circle has shrunk considerably, but idk. It seems difficult to start fresh with new people nowadays
Which is all to say i agree about needing mostly irl, but there is also something of online community that irl could never replicate (for most people).
I think the problem is not keeping agents out of private real people spaces, but for people who dont have any pre-existing or 'real world' connections to these communities to find a way to prove they are a real person over the internet alone and get an invite
On a related note, I think this is going to be the biggest challenge to most folks when it comes in resisting using government ID online. it will be the apple offered for easy proof youre not a bot to normal circles.