Y'know, as much as I DO like the idea going around that Eren reminds Levi of Isabel to a certain extent, I admit I don't like how some parts of fandom feel the need to shoehorn Isabel into nearly EVERY interaction Eren and Levi have and flatten their relationship into Levi looking out for Eren solely because he reminds him of Isabel
I’m gonna say that I very much agree with you. I have no problem seeing comparisons between Eren and Isabel as characters and their relationship with Levi, and they certainly have very similar spitfire attitudes that may very well remind Levi of Isabel when looking/listening to Eren. Plus...those eyes!!
However, I do think it’s a stretch to nitpick every interaction either of them had with Levi and form a connection there. Some are simply common attitudes toward Levi by other characters, such as respecting his strength and power and finding him a role model. And Levi’s behavior toward Eren differs vastly from his behavior toward Isabel. I think the majority of the reason he insisted being a sort of “big brother” to her was because he wanted her to avoid following a similar path like his own upbringing. She was vulnerable and near death and it was a very quick, committed decision and he never abandoned her since. In that manner, it feels like they have a more sibling bond.
The relationship between Eren and Levi, while based on trust, did not start the same way as with Isabel and the opinion of Eren was entirely different. He was inspired by the life within Eren. His concern for Eren developed beyond “commander’s orders.” While Isabel brings out Levi’s protective side he acts this way because he wants to take care of her, whereas his relationship with Eren is based on Levi supporting his decisions. I mean, yeah, I’m on the bandwagon of Levi’s incredulous expression when Mikasa insists on Eren’s survival in the woods was probably because of a vague memory of what happened to Farlan and Isabel when he abandoned them- he didn’t want Mikasa to feel the same nor did he want to give up on Eren (he doesn’t stop chasing the FTT even when he expresses the worst case scenario).
And to add, it’s very clear that Levi is, in fact, inspired by Eren’s fiery passion, as shown in future chapters and their VN. It just has so many layers that aren’t identical to the sibling relationship Levi and Isabel had. I’m not at all saying their connection is any less important and that Levi cares about one less than the other, but it’s ultimately very different. It’s cool that there are visual parallels and certain personalities traits that stick out between the two. They both tend to be aggressive, outspoken, rash, awestruck, and determined. But I think Eren is slightly more mature than Isabel and his life experiences have hardened him up in the face of violence (we don’t know much in the way of Isa’s experiences with death and whatnot, but she never saw a titan break and eat her mother). Eren might also be more ambitious, whereas Isabel is more defensive, streetsmart, and cocky. So even as individual characters, only their very basic personality traits are comparable. So it’s hard to imagine their relationship with Levi is extensively similar. It just...the story explains them both differently and I personally prefer the idea (well, I mean, it’s basically canon actually) of Eren being somewhat of a guiding light or hope in the eyes of Levi that he must ensure keeps burning for multiple reasons...and because he naturally does care.