This issue started for me at 5.4.2. There is a note in the change log that says "Improved export quality for high and max settings on machines with Nvidia cards."
Whatever this change was is most likely causing the issue. The exported video should not be larger than the original video.
Alternatively, it would be nice if there was an option to export the video at original quality, but still perform stabilization, export gmetrix data, etc.
My Setup:
Virb Edit 5.4.3
Nvidia Geforce GTX 1050
Using a Garmin Virb 360 camera