I have a very slow Internet connection (5 Mbps down, and even less for upload). Given that, I always download movies at 720p, since they have low file size, which means I can download them more quickly. Also, I don't notice much of a difference between 1080p and 720p. As for 4K, because I don't have a screen that can display 4K, I consider it to be one of the biggest disk space wasters.
Am I the only one who has this opinion?
To be fair, resolution is not enough to measure quality. The bitrate plays a huge role. You can have a high resolution video looking worse than a lower resolution one if the lower one has a higher bitrate. In general, many videos online claim to be 1080p but still look like garbage because of the low bitrate (e.g. like on YouTube or so). If you go for a high bitrate video, you should be able to tell pretty easily, the hair, the fabric, the skin details, the grass, everything can be noticeably sharper and crisper.
Edit: so yeah, I agree with you, because often they are both of low bitrate...