I know certain positions require that piece of paper, but in a hypothetical employment scenario, would an employer take the worker with exceptional experience and proficiency and minimal formal education, or the worker with enough discipline to earn that piece of paper?
This really varies by occupation. It’s hard to gain exceptional experience and proficiency without working in the field, and in some fields it’s hard to get that first job without some education or training. Once hired, some companies invest in growing their people and others not so much. For right out of high school, look for an apprenticeship program.
It depends. Many jobs do have educational requirements.
It depends on the kind of job. An obvious example would be jobs that require occupational licensing (e.g. certified public accountants, lawyers, physicians, most civil engineers, architects, etc.) versus those that do not (e.g. computer software developers, sales people, politicians).
However, even in the case where someone can be hired to a highly skilled job without the usual formal education, s/he typically has done extensive self education in the skills needed for the job. Such self education commonly requires a high level of ability and motivation; most people find it easier to learn the skills with the aid of instructors as commonly found in schools.
Probably depends upon the profession–are we talking bout a surgeon or a carpenter ?