The phrase "most has been" can be described using several synonyms. Another way to phrase it is "most accomplished", which indicates a person or entity that has achieved the most in a particular area or sphere. "Most achieved" or "most successful" are similar synonyms that convey a sense of accomplishment and recognition. For those who want to emphasize the effort or hard work required to reach this level, "most dedicated" or "most committed" are appropriate synonyms. In contrast, those who want to emphasize the influence or impact of someone may prefer "most influential" or "most impactful". Finally, "most experienced" may be the best synonym if you want to focus on the years of learning and expertise under one's belt.