I think what Elliot means by "the same" is that they are both when pressed more likely to blow the world up in anger than they are to productively move on from their pain.

They are both (when triggered by injustice) akin to that Burmese bandit Alfred (Michael Caine) describes who does bad deeds "just to watch the world burn" in the movie The Dark Knight Rises. Only in the case of Elliot and Carla, it is not pure nihilism that motivates their excesses, it is a desire for revenge/justice. But in both the case of Elliot (five/nine) and Carla (blowing up a row of cars to get revenge on the man who was rude to her in a club) the problem is in the large collateral damage such revenge/justice left in their wakes.

Carla smiles when she is reminded of blowing up the row of cars as if it was worth it to blow up the cars of a number of innocent club-goers and go to jail as long she got the car of that asshole (or at least that she can shoulder whatever guilt came with her explosive decision).

With Elliot, in order to get revenge on E-Corp for what they did to his Father, he was willing to plunge millions of people into poverty in the name of "saving the world." In a way, Mr. Robot (Christian Slater) represents the constant possibility of violence inside Elliot's fractured psyche. Mr. Robot represents the "Animal Man" and Elliot the "Spiritual Man" from Tolstoy.

In fact, Mr. Robot wears Edward Alderson's face because like his own spiritual and animal sides are fractured into distinct personalities in much the same way he cannot find a way to both mourn the loss of the parts of his Father he loved and make peace with the parts of his Father he hates. Elliot is constantly confronted by this schism represented in the violence of Mr. Robot's attacks. Mr. Robots personality is really just the itch he can't scratch, the part of him that wants to "watch the world burn."

Elliot is protective because he sees his failure to protect his from Mom in the ongoing drama between Carla and Santos. He wants to connect to her like he is connected with Darlene (Carly Chaikin) and he wants to protect her (and almost everyone else in his circle) to make up for how he failed to protect his sister Darlene.

Of course, he also has an intense narcissism, but as I have suggested before, it is most likely protective narcissism (I am the center of the world because it protects me from other central figures hurting me).

But there is one other element here, he is trying to connect to Carla to distance himself from the darkness he sees in himself. Elliot has said "I am Mr. Robot and Mr. Robot is me" enough times by now that we should understand that he fully gets that Mr. Robot represents his own animal desires.

When Elliot decides to visit his Mom in Season 2, it is totally unsurprising that Darlene has no desire to join him. But, why in the world would Elliot want to see his Mom given what he knows she did to Darlene (and occasionally to him). This is the face in the mirror that makes Elliot "hate himself" as he said in the June 7th entry of Red Wheelbarrow. He sees the dark part of himself, like the dark part he saw in his Mom and Dad, every time that Mr. Robot shoots him or helps him realize his plans for revenge.

Elliot's problem is that he knows deep down that Mr. Robot always wins because, like Carla when she smiled, he really does want revenge, five/nine really did make him happy, and he really does know it is wrong to want the things he really truly and deeply wants.

As much as he wants to protect people like Darlene and Shayla and Carla, at the end of the day, he wants his plan more.

Shayla was a casualty of Elliot's plan, Darlene is on her own at massive risk trying to run fsociety while Elliot cools his heels, and Santos is still wandering the halls of the jail with hatred in his heart for both Carla and Elliot.