This is right from the horse's mouth at Morningstar:
"Morningstar Manager Research
Feb 24, 2025
Mutual of America has a strong investment culture as a firm, resulting in an Above Average Parent Pillar rating.
One of the most notable selling points of Mutual of America is its favorable fees for open-end and exchange-traded funds, signifying a dedication to investor interests. The firm's fees across their funds, on average, fall into the second-cheapest quintile of peer strategies. The firm's lineup has been durable. It has had a 10-year success ratio of 68%, meaning that of the strategies with a 10-year track record, 68% have beaten their respective category median. A high success ratio provides us insight into the relative success of the firm's product offerings. Mutual of America has undergone a bout of turnover in the past five years, as seen in its lower-than-average portfolio manager retention. Turnover in the portfolio-management ranks can happen for a number of reasons, including mergers and liquidations, portfolio managers moving into other roles, or portfolio managers leaving the firm. In some cases, such change may not signal a serious or immediate problem at the firm, but can still be disruptive for investors, hinder the effectiveness of a firm’s investment processes, or suggest a weaker investment culture."