Learn English – Antonym/Opposite of “Legend”

Perhaps relapser.

n. One who relapses, as into vice or error.

It is usually related with illnesses but it is also used for people who relapses back into addictions. There is a term called "chronic relapser" for these kind of addicts as well.

From Addiction Professional magazine:

Numerous failed attempts at sobriety, or a return to drugs/alcohol after a substantial period of sobriety.

While this is a simple and obvious criterion of a chronic relapser, the distinction of an individual who has attempted sobriety and failed is important.

Many addicts have a lifetime of drug and alcohol abuse but have never actually attempted to get sober. What makes chronic relapsers distinct is that they have tried and failed.

What about something like "layabout":

a lazy person who avoids work

This term may lack the explicit concept inherent in perfectionism (the need for everything to be perfect) but I would think that a person who "avoids work" is quite the opposite of someone who goes to extra effort to make something perfect.