Yeah that stuff I myself got rid of back in the Gnome 1 days when you could still customize all that. I appreciate that the Gnome devs came to the same conclusions as me.

• Desktop icons are usually hidden behind windows. It makes more sense to put launch icons in front of everything else, like Gnome does when you hit the Win/Super key.
• Minimize is unnecessary when you have workspaces and efficient window switching methods. Same for the task bar.
• A long time ago, when I was young, I played around with themes and shit, when that was still supported. There were always problems. Theming any complex set of applications yourself is basically impossible without causing issues, and themes made by others also exhibited this problem. You need a concerted long-term effort, plus buy-in from basically all app development teams, to make a comprehensive theme. Note how Microsoft/Apple don't want to support theming either.
• Systray was always some excuse for apps to just keep running in the background while not taking up taskbar space. Steam can go fuck itself, just please exit when I ask you to, and don't treat the close button as "minimize". If I wanted Steam running in the background I would just put it on another workspace.

• I'm not sure what you mean. Lack of desktop icons is only valuable to people who want that (I don't, and I remove them on my Plasma systems).
• Gnome has a minimize button, and you need only turn it on in Tweaks > Windows.
• You can change themes in Tweaks > Appearance, and you can install themes by script or by manually dropping the files where they need to go (something you sometimes have to do on Plasma, too).
  • You can further adjust themes with extensions or scripts. Unless you change themes often, quick theme swapping is not a feature everyone needs or wants. How often are people doing this IRL?
• I can right click all my menu and dash/dock icons and get an app-specific context menu, so I'm not sure what you mean with this gripe.
• Systray is one of the things I don't like about Plasma, and I wish they'd find a different solution. It's bad enough on Windows.

I run both DEs on different systems, and they're both good and bad at different things, but they both have comparable feature sets. Their workflows are different, yet you can do virtually all the same things in each.