Gross Return vs. After-tax Nominal Return

"Thus, gross return is an appropriate measure for evaluating and comparing the investment skill of asset managers because it does not include any fees related to the management and administration of an investment"

VS

"taxable investors evaluate investment managers based on the after-tax nominal return."

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Question:

Both claims being appropriate to evaluate asset managers performance, but Gross Return is before tax, and After-tax Nominal Return is after tax...

Is there any contradiction, or how to understand both means are appropriate to evaluate asset managers?

Thanks!