On the other hand you can just install KDE Plasma that went a long way and works fine if you just stick to the UI - all your pain points should work out of the box or can be configured using systemsettings. KDE applications are a mixed bag - I love dolphin but kmail and other stuff feels strange. Also printing is way better in GNOME apps, not sure why exactly.
I'm on a laptop most of the time and, like you, have absolutely no desire to go back to wasteful non-global menus. Have you eyed a replacement DE for Unity/Ubuntu going forward?
Edit: OTOH, Ubuntu have clearly spent a good amount of effort to customize Gnome so here's hoping they can morph it to work like Unity even more (OHD, global menu)
Global Menus is unfortunately something that I still miss, although I was able to recover some screen space with an Extension called Pixel Saver, which merges the window control bar with the panel by removing the window decorations and adding the buttons to the panel. Not ideal, but useful.
So, when you have your hand on the keyboard, this can be much more convenient.
I've got the exact same 1440p screen as you on my Thinkpad (which wants to be run at 1.5x or 1.75x) and the best solution I've found is provided by KDE. Try installing Plasma (either by installing Kubuntu or just installing the desktop w/ apt) and setting Display->Scaling to 2X and then go into fonts separately and set "force font DPI" to 168. That's working remarkably well for both GTK and QT apps for me. 2X scaling for windows/icons keeps them from being tiny/blurry and setting the font size to 168 (aka 175%) prevents the fonts from being huge.
The Mutiny layout in UbuntuMATE 18.04 is really nice, and they've implemented the HUD, global menu, titlebar integration, and it's got HiDPI support now.
I think multimonitors is still an issue though - you can only have one dock, and it's best left on the screen on the left by the looks of it.
I kinda tolerate gnome 3 (despite its marvellously obvious flaws) for now and if I find it way too annoying, I'll rip it out and use fluxbox or smg similarly low level wm.
I've tried Gnome and was very disappointed. No global menu integration which means losing useful screen space for no good reason. Tray icons somehow look squished and ragged. No fractional scaling is a massive issue for me since I'm working with dual 27 inch 4K displays. Tray bar only shows only on one of the monitors and you need a plugin to make it appear on both which is just ridiculous. No more convenient built in features/options like auto resizing a window to 1/4 of the screen by dragging it with a mouse to one of the corners, etc.