Before answering the real question, let's at least point out a little misconception your post seems to make. There is no real indication that the map chooses who to send on a specific mission based on the "element" alone. Personality seems to be involved too - for example the map seems to have avoided sending Pinkie in when her exuberant personality may represent a problem (imagine Pinkie being choose in "The Sound of Silence" for example...).
As for the rest, this is obviously spoiler for the specific episode you mentioned, so I will use the spoiler markup even if the episode is quite old by now.
Let's start with a clarification: Starlight "plan" was never about "Equality" - notice how she never gave away her Cutie Mark for example.
Starlight resentment against Cutie Marks and the "individuality" they represent is born from her own past - she had a friend in Sunburn and she "lost" him. In her mind, Sunburst getting his Mark and going to magic school is what stole him from her.
Therefore, Starlight isn't using "Equality" as a way to make everyone equal. Her real aim is to remove the cause of her lost - the Cutie Mark represent the "ambition/vision" of a pony and that vision is what drives a pony to pursue his dreams even if that dreams takes them away from her. As she says in her song "You can't have a nightmare if you never dream".
So, just to be clear. Starlight plan is not about "Equality" as in "everyone is equal and has the same rights". The story isn't either a retelling of Animal Farm nor - despite what many seems to believe - an attempt at analyzing ideas related to real-world Communism. A better comparison would be Kurt Vonnegut's short story Harrison Bergeron ([full text available here, link taken from Wikipedia) - a dystopian story about people wearing external handicap devices to strip them from anything that made them different.
For that reason this story also isn't a story about people realizing that they could be more happy if Social inequality was abolished: those are just Starlight claims to try to sugar coat what is really happening.
Under Starlight facade the reality is different. Ponies are unhappy, force coerced into an idea of abandoning their dreams so that no one will ever get away again. You see forced smiles during the "Our Town" song, you see desperate attempts to comb your mane in a different way being immediately stopped... you even see a prison used to subdue ponies into giving up to the "Equality" fake ideal. What Starlight is trying to achieve is not Equality. Starlight wants an Immovable Eternity, unperturbed by any dream or exception that may take anyone on a different path, a path that would take them far away just like Sunburst. Her world must be a static one, one where nothing changes - only then she may be sure that she will never have to say farewell again.
It should then be clear by now that the map isn't sending the ponies on a mission to fight against the idea of Equality. The Mane Six are sent there to help the suffering ponies that live under Starlight decree. And to help Starlight - a pony that raised a wall around herself in a desperate attempt to never have to suffer a loss again.
If you ever have the chance, I suggest you read the My Little Pony official IDW comic arc called "Siege of the Crystal Empire". You may notice some similarities about Sombra's story in the comic and what Starlight went thru.