Some of these examples are not equivalent. For example,

    r
      .db('dragonball')
      .table('characters')
      .filter(function(row){
        return row('maxStrength').gt(700000).and(row('species').contains('Saiyan'));
      })
      .orderBy(r.desc('maxStrength'));

presumably returns one row per character, whereas

    SELECT c.* 
    FROM characters c
    INNER JOIN character_species cs ON c.id = cs.character_id
    INNER JOIN species s ON cs.species_id = s.id
    WHERE max_strength > 700000
    AND s.name = 'Saiyan'
    ORDER BY max_strength DESC;

returns at least one row per character. Rather, the equivalent SQL (depending on what syntax is available) might be:

    SELECT c.* 
    FROM characters c
    WHERE max_strength > 700000
    AND EXISTS (SELECT NULL
                FROM character_species cs
                INNER JOIN species s ON cs.species_id = s.id
                WHERE c.id = cs.character_id
                AND s.name = 'Saiyan')
    ORDER BY max_strength DESC;

The above returns one row per character, no matter how many matching entries there are in `character_species` or `species`.

Pursuing this a little further then, suppose you wanted to expand your search to include humans and androids. In SQL, only a slight modification is needed:

    SELECT c.* 
    FROM characters c
    WHERE max_strength > 700000
    AND EXISTS (SELECT NULL
                FROM character_species cs
                INNER JOIN species s ON cs.species_id = s.id
                WHERE c.id = cs.character_id
                AND s.name IN ('Saiyan', 'Human', 'Android'))
    ORDER BY max_strength DESC;

I shudder to think what that would look like in functional form. Something like this?

    r
      .db('dragonball')
      .table('characters')
      .filter(function(row){
        return row('maxStrength').gt(700000).and(row('species').contains('Saiyan')).or(row('species').contains('Human')).or(row('species').contains('Android'));
      })
      .orderBy(r.desc('maxStrength'));

But how would it know how to group the disjunctions?

In my very limited experience, examples like these always look so tantalizing until you start taking them a little further and then you quickly realize there's no such thing as a free lunch. In this case, you pay for the flexibility of RethinkDB with the expressiveness SQL.