I've gotta say man you have a really interesting mix of knowledge and obliviousness. Not a bad thing, it's just interesting. I'd never have guessed that a tech guy who works in NFT stuff would never have heard of Discord, much less one who plays video games (and participates on a video game forum) yet doesn't know that in-game voice chat is a thing.
It's our differences that make us interesting lol.
I consider this as him having trouble climbing over inconvenient obstacles. It's never really been an issue for me personally. Could be worse, e.g. many shrimps have you die immediately upon touching any such obstacle.
*shrug*
Security and style of display are not intertwined in that way. Having a subdomain for a better view on mobile isn't a modern way of doing it, but it's not technically wrong. Sometimes it's simply a matter of an old dude just doing what he knows. It's not inherently insecure or anything like you imply.
There are sites still made which will detect and redirect you to, for example, m.website.com. A subdomain dedicated solely to a mobile display. It's a very oldschool way of handling it.
Not "for some reason". For a good reason.
Images are technically heavy, bandwidth wise. Loading a smaller image on mobile is the status quo on the web, and rightly so for load time, accessibility, etc..