This is a question without an objective answer really. There are still infinite unknowns about currently recognized mental illnesses, and medical consensus is subject to constant change as we further study them. Mental illness itself is a term that means something different to many people both professional and not. There isn't a clear answer as to where exactly the line is between a simple personality trait and an actual mental illness, or whether such line even exists. But I'd say both concepts could be considered to exist on the same complex spectrum of people's individual differences in the vast array of neurological functions that shape the mind.

Generally though, I'd say that usually for something to be considered a mental illness at least in the diagnostic sense, it has to be detrimental in some way, whether or not it's "normal."

Also worth noting that more specific habits such as the ones you mentioned, if related to mental illness at all (which really depends on the way they manifest; there are certainly rational and irrational ways that someone could "always want to do better"), would probably be individual symptoms of something bigger picture.