This may be a necro but you can run reshade with D2DX (works with launcher too)
Why use D2DX?
To get these features: higher FPS cap, better scaling (there still black bar but you game fills the whole screen windowed mode now)
Step by step:
0.5. Choose glide in median launcher
1. Install D2DX
2. Configure D2DX: DISABLE RESMOD (follow instructions in the D2DX thread)
3. Install reshade. Choose DirectX for render (because we use D2DX)
4. Use ini file at #1 of this thread when being asked for config
5. Done
Result:
https://imgur.com/a/LZdsYihD2DX:
https://github.com/bolrog/d2dx/releases (just get the latest version)
D2DX thread in the forum:
viewtopic.php?f=42&t=66782Reshade:
https://reshade.me/#download (non add-on, can use latest version instead of the one at #1 here)
PS: technically you can do the black bar filling but I haven't researched yet (2k monitor)