Yes. I do believe an external 4k 27" on a laptop is used differently than a single screen on an iMac. I also believe people use iMacs in ways that are different

Yes. I do believe an external 4k 27" on a laptop is used differently than a single screen on an iMac. I also believe people use iMacs in ways that are different than what you use, which was the whole point of my answer. People use screens in all sorts of different ways. Most of them have resolution requirements much below yours, which is why the market apparently doesn't cater for your needs.