Ohm v2, 16 bytes

²Σ½¬³Π¬³Σ½D³Πs/Σ

Try it online!

Explanation

square sum halve sqrt input product sqrt input sum halve dupe input product swap div sum

...if Ohm had a verbose mode of sorts. :P

²Σ½¬³Π¬³Σ½D³Πs/Σ

                  implicit input       [[7, 6]]
²Σ½¬              root mean square
²                  square              [[49, 36]]
 Σ                 sum                 [85]
  ½                halve               [42.5]
   ¬               square root         [6.519]
    ³Π¬           geometric mean
    ³              push first input    [6.519, [7, 6]]
     Π             product             [6.519, 42]
      ¬            square root         [6.519, 6.481]
       ³Σ½        arithmetic mean
       ³           push first input    [6.519, 6.481, [7, 6]]
        Σ          sum                 [6.519, 6.481, 13]
         ½         halve               [6.519, 6.481, 6.500]
          D³Πs/   harmonic mean
          D        duplicate           [6.519, 6.481, 6.500, 6.500]
           ³       push first input    [6.519, 6.481, 6.500, 6.500, [7, 6]]
            Π      product             [6.519, 6.481, 6.500, 6.500, 42]
             s     swap                [6.519, 6.481, 6.500, 42, 6.500]
              /    divide              [6.519, 6.481, 6.500, 6.461]
               Σ  sum                  [25.961]
                  implicit output      [25.961]