Well Pingu, I notice two things, one of which I complained about.
FIRST. Both computers are powerful, “deceptively modern,” but not enough to work with very large encoded 4K files.
SECOND. If you work with resolutions higher than FHD, you’re always going to get stuck with the filters, even if it’s a great machine.
THIRD. If the video is for personal use, don’t export it in h264/HEVC.
In my basic experience, Shotcut 
reminds me of Open Movie Editor, a dead project. In fact, the author recommended AVS Video Editor to its users.
It works quite smoothly, even in previews with filters, and allows you to quickly stabilize videos in parts. In fact, my computer is similar, a 2013 model.
