Yeah the windows are a little annoying to supply, especially if you also have electric window upgrades installed… then it requests 5 Windows and 1 Servo… and that is pretty much overkill for the Resource Importers, especially if you have more than one Fit Windows Slot.
I think that the Rear window should probably be its own slot… “Fit Rear Window” where the rear window gets attached (maybe even with upgrades like Heated Rear Window for unfreezing the window during winter etc).
And maybe also split up the steps for the side windows… front side windows and rear side windows… also each with their own upgrade capability to install electric windows.
That would alleviate some of the throughput bottleneck.
But there also has been some discussion that the windows should be installed into the door panels directly as a sub-assembly stage and then put the entire door (including the installed window) on the car in the “Fit Doors” stage… which would be more like it actually happens in real life.