You're focusing on Eren becoming genocidal, but the reason he becomes genocidal has nothing to do with what he truly desires and everything to do with the resources they have (i.e. the Rumbling, and literally nothing else) juxtaposed with the threat they're up against (i.e. the entire world) and the fact that literally nobody else came up with a better idea to even postpone this threat that wasn't "make breeders out of Historia's whole family line" or "spay and castrate every Eldian so they die out" (which doesn't even guarantee their short-term safety).
Your idea is varyingly viable. Disregarding that Eren is intrinsically foolhardy to the point that "suicidal bastard" is the nickname he received during training and so "the constant threat of death looming over him" wouldn't have effected as much as it would other characters given his goals and drive, emphasizing the negatives of his experiences could work... but everything else is meh.
He can't consistently be a freak and be the person everyone's putting their hopes on to the point that they're aggressively throwing away their lives to protect him and/or facilitate his part of the mission, or else you also have to show the inevitable impairment of military activity as a result of this as well as contend with the idiocy of people who think that way even after he becomes competent with his ability. It also means that you have to tweak the characterization of the Survey Corps from "a gaggle of eccentrics", which is a trifle, but still something to consider.
Given the conflict and Eren's character, I don't know what you would pick at in order to emphasize Eren's being used as a pawn-- he wants to kill Titans and free humanity. Erwin also wants those things. He's also a soldier of barely any rank, so he was already a literal pawn.
Erwin pitting a possible confrontation with the Female Titan in the Stohess district could be an experience used in service of building Eren's insecurity with being a pawn, the aforementioned aside... but that incident is on the heels of us coming to an understanding that Erwin's MO for victory is to sacrifice everything that needs to be sacrificed, and his willingness to do this even if the plan could fail was meant to emphasize that trait, which is also meant to be the prevailing morality of the setting. Not only that, but the reason why soldiers or civilians are dying in Eren's vicinity whenever he gets to Titan business is either as collateral damage or in defense of his part of the mission-- he actively "benefits" from this, and is repeatedly reminded that lots of people are being fed to Titans because they're also staking the victory of humanity on his shoulders, so where exactly would any animus regarding this be directed?
Himself? Well, that much happens, particularly when he discovers that the power of the Founding Titan is inert within him and humanity could have allegedly claimed victory against the Titans with a snap of the fingers if the power dwelt within one of royal lineage.
You'd rightly argue that leaving most of the Corps in the dark about the giant trap they had for the Female Titan in the Forest while they were getting slaughtered would be adequate demonstration of this, but I'd argue that engineering a situation where civilians would likely become collateral damage in a setting where this would be called out drives that point in even more harshly.
Well, I would call it "fucking metal".
Oh, we're... we're talking about the pairing overall.
Yeah, yeah, "inseki" it is... especially since she was only part of the family for like, a year before they lost both their parents, so she may as well be a "childhood friend".
The problem, as discussed before, is that everyone would have to lose about 100 IQ points and be completely retarded for Eren genocide to happen as is. Eren has to be retarded, and everybody has to be more retarded than Eren. The entire fact that his plan was genocide is a literal 'WTF' moment. In the manga, for YEARS, it was acting like he had some big plan in the bag. That's why the huge meme on /a/ is "TRUST THE PLAN", referring to Q Anon, who was never right about anything and had no plan.
We have no real idea WHY Eren chose genocide. He tells everyone its the only path, but why? You don't need to kill the entire world. You can easily cripple it. So why kill literally everyone? There's no answer given. There's no indications its a Lelouch gambit, because honestly, there's just too much death for it to be one. That's just assumption.
Like, if you blew up the world's power grid and energy producing facilities, all of them, it'd set them back to zero. It'd take a bit of time, but you can do it without fucking killing everyone. You can target infrastructure, military targets, warn cities and have them stomped, by making everyone leave. You've got four years and a metric ton of sky scraper titans, and the best you got is "FLAT EARF HURRR". Its idiotic. By the time the rumbling happens, the military on Marley is entirely crippled. Nearly everyone competent in it is dead. Cleaning up assets and killing heads of state to throw the world in a state of anarchy would be piss easy. There a thousand ways to cripple the world without having to kill millions of people, but the fact that his plan is so retardedly simplistic after being lead on it was some grand scheme is hilarity.
What's even more hilarious is that for everyone in the scouts, NO ONE, NOT ONE gives him an alternative option. They hem and haw and go "But that is wrong Eren." He's literally screaming in their faces to give him something, literally fucking anything, and they don't. They don't give him a single fucking thing. Which means while Erens idea is fucking retarded, everyone is more retarded than Eren because they cannot think of a single alternative idea.
The fact that they cannot give him ONE alternative other than to 'talk with them' (which would just buy them time to build up their forces to murder them, as shown the world are racists to the point of pathological retardation) and Eren basically says is useless. And while Eren is completely unreliable as a narrator, we know its useless because we've seen it. And that's ALL they can give him. Diplomacy. Are you fucking kidding? They put you in a fucking CONCENTRATION CAMP for TWO HUNDRED YEARS, tortured you and fucking LAUGHED about it. You think they're going to fucking negotiate?
It defies belief that everyone in the Scouts and the military is so fucking incompetent that they have absolutely no alternatives to give Eren is ludicrious. Of course in this scenario where everyone is fucking retarded he's going to choose genocide.
Eren feels like a pawn because nobody takes him fucking seriously and idiotically, constantly disregards him and his warnings. Again, this only works if everyone is a fucking retard. You've got a living weapon and a guy who can see the future says that, barring nothing changes, all of Paradis dies, so help him out. They just lock him up and go "Well, we'll try diplomacy with a society that feeds little girls to dogs and has rape camps and has tortured us for two centuries even though we had nothing to do with anything. Bye."
That's it. That's their grand fucking scheme. Its hilarious to me that when they infiltrate Marely and these guys are STILL indoctrinating people about geocoding them, forcing people to wear fucking armbands and live in camps, Eren's the only one to come away with "Well, fucking talking isn't going to work." That should have been EVERYONE'S take away. Then you have them be utterly shocked when Eren pulls a fucking Dresden. Yeah, no fucking shit Eren is going straight to fucking war.
"Oh no, Eren killed the children." Give me a fucking break. How many children are Marley responsible for killing, directly and indirectly, in FAR worse and more inhumane ways? He's going to fucking war. You've given him no options. War is obvious and inevitable and civilians are always caught in the middle. Yet everyone keeps shitting on him and giving him no alternatives, which completely kills suspension of disbelief. This is the real reason people wanted Eren to win, because although Eren was retarded, everyone else was much more retarded.
The genocidal idea belies logic, because everyone would have to be a fucking idiot for it to happen.
Well, i certainly imagined worse, I thought Eren was kissing Zeke.
