For reasonable bitrate/resolution pairs, both matter. Clean 1080P will beat bitrate starved 4K, especially with modern upscaling techniques, but even reasonable-compression 4K will beat good 1080P because there's just more detail there. Unfortunately, many platforms try to mess with this relationship, like YouTube forcing 4K uploads to get better bitrates, when for many devices a higher rate 1080P would be fine.

Try comparing a 4K vs 1080p that were created from the same master, like a modern Criterion restoration.

Without HDR the differences are negligible or imperceptible at a standard 10' viewing distance.

I'll take it one step further: a well-mastered 1080p Blu-Ray beats 4K streaming hands down every time.

It very much depends on the particular release. For many 4K releases you don't actually get that much more detail because of grain and imperfect focus in the original film.