No it's not 1080p tall? The image is 945 pixels tall, including an extensive box shadow. I'd wager that it's around 800 pixels high. The font also looks significantly bigger (esp taller) than it is on my machine.
Additionally, the search panel is usually not folded out. You can also move it to the side at your discretion (although I don't think the Kate search pane is very well suited to that). In Kate I also remove the toolbar so that I only have the menu bar, since new/open is rare for me (I use the file tree), save is just ctrl+s, and undo/redo is also something I use keyboard shortcuts for.
I don't use Kdenlive, but I don't see the problem for the clip problem list window either. Maybe the buttons on the side might be better located at the bottom, but that's it. The only real problem is that the window should probably be larger than it is on the screenshot, however it looks like you can freely resize it.
Finally, the things you mention are not related to the theme at all, but instead the layout of individual applications.