That is completely wrong. Spread by graphs based on nothing.
A 4k screen unlocks higher bit rate content which is much clearer for a start. The difference in the quality of the source is increased massively.
Then the fact is everyone has different vision. I have better than 20/20 and I've always been able to see signs and read stuff from miles away. I've had eye tests done and the different opticians have all told me my eyesight is perfect.
So I can see the difference of 4k on a 43" screen from 9 feet away easy.
People need to stop spreading the myth of you needing at least 50 inches to see 4k.
The higher bit rate content can be easily distinguishable against its 1080p counterparts.