Which is also flawed when you stated...
No, he's not. The moment we meet him, he's dead set on revenge. When he blew up London and attacked Starfleet HQ, he did it because he believed Marcus had killed his entire crew. He openly admits this.
KHAN: I had no choice but to escape alone. And when I did, I had every reason to suspect that Marcus had killed every single one of the people I hold most dear. So I responded in kind.
And if you still think saving his crew was his only motivation, don't forget that after Khan realized that his crew are still alive, he didn't tell Kirk or anyone else about how to open the torpedoes that actually contained his crew. Nope, nothing about how to avoid the self-arming booby trap or the circuits to diffuse the bloody thing. He just risked one of his crewman that he holds DEAR.... for no reason. There's no way he couldn't have known about the Booby Trap because those torpedoes were designed by him.
Again Jeyl, you have to focus on motivations, not superficial similarities.
In TWOK, Khan's vengeance is motivated by the events of Space Seed and the ensuing decades of being marooned. His conflict with Kirk is intensely personal (which they beat you over the head with when Khan quotes Moby Dick). He is so motivated by vengeance, that he is blinded by his rage and dispenses with reason (Joachim tries to beg him off, but he persists to kill Kirk).
This is not what happens in STID. STID plays off Marcus and Khan. More to the point though, let's look at that exchange:
James T. Kirk: I watched you open fire in a room full of unarmed Starfleet officers. You killed them in cold blood.
Khan: Marcus took my crew from me!
James T. Kirk: You are a murderer!
Khan: He used my friends to control me. I tried to smuggle them to safety by concealing them in the very weapons I have designed. But I was discovered. I had no choice but to escape alone. And when I did, I had every reason to suspect that Marcus had killed every single one of the people I hold most dear. So I responded in kind. My crew is my family, Kirk. Is there anything you would not do for your family?
I don't think it's at all clear from this passage of dialogue that Khan is talking about London. Kirk is clearly talking about the attack on Starfleet HQ. Even if we want to say that he's talking generally about his actions, for you to argue that Khan is not interested in saving his crew is, quite simply, ridiculous. That's Khan's motivation for the second half of the film.
This parallels much more with Space Seed than TWOK.
Marcus and McGivers are both fascinated with Khan and extend trust to him because of this fascination.
Khan has no reason to be "vengeful" against Kirk in Space Seed because Kirk did not freeze him and send him out into space. He attacks Kirk because Kirk is standing in the way of what he wants: the ship.
Likewise, in STID, Khan has no reason to be "vengeful" against the Enterprise. It's quite clear his beef is with Marcus. The Enterprise is just in the way. He manipulates Kirk and the crew of the Enterprise in an attempt to
rescue his crew, in a similar manner in which he manipulated McGivers into helping him take control of the Enterprise.
When Khan kills Marcus and takes the Vengeance, what does he do? He asks for
his crew. Spock refuses, so Khan says he'll attack the life support systems and suffocate the crew of the Enterprise and get the torpedoes later. Hmmm, where have we seen Khan try to suffocate the crew of the Enterprise before...? Oh yeah, Space Seed!
The point being is that TWOK is about Khan pursuing Kirk. In STID and Space Seed, Khan and Kirk interact, but in neither is Khan's primary motivation to kill Kirk.
