split, by default, operates on $_, but the elements of @bigarray are references. You need to explicitly dereference them and then split the elements. That's why the internal map is necessary. Your suggestion leaves @bigarray looking this way:

$VAR1 = [
          [
            'ARRAY(0x504290)'
          ],
          [
            'ARRAY(0x531f00)'
          ],
          [
            'ARRAY(0x531e60)'
          ]
        ];
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