Outright, out-and-out, unmitigated, arrant are comparable when they are used hyperbolically as meaning not limited or qualified.
They are often used interchangeably as intensives, but there are clear differences in meaning.
What is outright has gone to the extreme and can be made neither better nor worse or is past recall.
What is out-and-out is completely as described at all times or in every part or from every point of view.
What is unmitigated is or seems to be so utterly what it is as to be beyond the possibility of being lessened, softened, or relieved.
What is arrant is all that is implied by the term that follows (usually a term of abuse).