To be fair to your first point, if you set up a bouncer or use a client inside of screen/tmux you can absolutely catch up on what was said earlier in IRC.
Really? I just leave irssi running on my linode, I don't even bother running a local client most of the time, I just SSH in and use it. The only exception is when I'm on mobile, and I have irssi-proxy running for that one special case.
I think part of this debate is that for some people, the above is a pretty normal and easy way of doing things, and for others, it's a large barrier to entry.
Really, having a $10 VPS and using screen or tmux is "uber-geek"? Look, if you can code in virtually any programming language I'd like to think you have the ability to use screen and irssi in under 10 minutes. We are talking specifically about open source projects, not general IM across a business (though I'd still use IRC there, just give everyone hexchat/xchat/whatever nice GUI client you want).
For end-user support people are still more than capable of using a desktop IRC client, as evidenced by the WEALTH of people that ask questions on #fedora, #debian, #ubuntu, etc every single day.
No, having a cheap VPS handle automatable tasks isn't ubergeek.
Setting up Node-red on a VPS, and logging a dozen IRC rooms you're interested in, storing in a MongoDB, and creating a search DB... over TOR is being an "uber-geek".
And it took me 10 minutes to set up. No programming required, interestingly enough.
We're talking about chats for open source programming projects, not the local book club. In that context, setting up an IRC bouncer or running a command line client in tmux on a VPS is not really a high bar.
Which is additional configuration to pay for and/or take the time to set up. And that you have to think ahead enough to realize you need this before you actually need it.