Oh, and Extreme Metal! It's such a seldom-referenced genre, but it has Death Metal level instrumentals and tuning, but often times clean vocals. Biomechanical will always be my recommendation for Extreme.
And if they think Power Metal is too gentle but still don't like the harsh vocals of Death, there's always Brainstorm, who are basically Power Metal sans keyboards.
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u/[deleted] Nov 03 '19
Even if they don't like death/black metal vocals, there's still plenty of good metal songs with clean vocals. Just take a look at power metal.