Help! Final Cut Pro File Size SOooo BIG!

Is there any way in Final Cut Pro to reduce the file size when exporting, WITHOUT decreasing the resolution?

This has been one of the first problems I noticed after first getting Final Cut to replace iMovie (for some reason the export file is always HUGE compared to my expectations), but it wasn't this big of a problem until I needed to share video productions with other people recently.

Today, I received a 2.33 GB 1920x1080 footage which only required me to add 1 transition to the beginning (super simple edit and shouldn't really affect the file size). I did just that, and when I tried to export it in the same dimensions & resolution, the size went up to 7.24 GB!

This made me quite confused, so I created a new, empty project and dragged in the 2.33 GB file. I didn't do anything to it this time and went directly to export––– 7.24 GB again. I've tried all possible ways (including the share to YouTube & Facebook feature, which couldn't get the size to be less than 7.24 GB). I also tried Compressor and 7.24 was somehow the minimum.

Calling Apple Support for >20 mins couldn't solve this problem. The Support Team member tried the same thing using one of their footage and computers. Same problem occurred: any footage added to Final Cut automatically scales up in size even if you didn't do anything with it. Why does Final Cut videos have to be so big in size...They didn't know either and advised me to seek help from the forum.

Thanks in advance to anyone who's willing to help!