When it comes to editing 1080P video on a 4K timeline in video editing software, the 1080P video will not necessarily look better. While it's true that working with a higher resolution timeline can offer benefits such as increased flexibility in terms of repositioning and resizing footage, it doesn't inherently improve the quality of lower resolution footage.
In fact, if you're looking to output your final video in 1080P, it may be more efficient to edit on a 1080P timeline. This is because working with a lower resolution timeline can result in better playback performance, which can be especially important during the editing process. Additionally, if you're working with 4K footage on a 1080P timeline, you can still take advantage of the higher resolution footage by zooming in or repositioning it as needed. However, it's important to keep in mind that upscaling lower resolution footage to fit a higher resolution timeline may result in some loss of quality. Ultimately, the decision to edit on a 4K timeline or a 1080P timeline will depend on your specific workflow and the specific requirements of your project.