You found that you had to download too much bloat to use Okular so you made an Electron app? Im pretty sure you dont have to download all of KDE to use one of its apps, just the package manager and the libraries Okular uses.
From a quick check now it is possible to install individual applications (Okular is not there):
https://community.kde.org/Windows
But it's not the same thing. At the times one was able to install the while kde4. That's a cross platform app!
(I haven't tested it -- happy Okular Linux user here. It was linked from the site you linked, though.)
Okular is ok as long as you run only linux. In theory you could run it also on macOS or Windows, but you have to jump through the hoops. That's not optimal for a productivity application.
It's not all of KDE, but...