Fanon Will Byers is Canon Lucas Sinclair
Caring, gentle, empathic, and selfless. Is how I've seen people describe Will even stating that hes the most caring on the show.
This is more like the description of Lucas though, and thats been clear since season 1.
In Season 1 Lucass character is by far the most concerned with finding Will. With Mikes time being split between protecting El and finding Will. Lucas only suggests they rehome El because he wants to get back to finding Will immediately. Why does he blow up at her in the junkyard? The same exact reason, he thinks shes sabotaging their mission to find him, so he blows up. However what he does after proves he is much more capable of being empathetic then Will is.
Lucas scopes out the lab on his own, and reports back that they are coming for El, even while being mad at her. Then HE apologizes first, getting down to her level and gently explains he was wrong. He then gracefully accepts Mikes apology.
Season 3 is where the difference between these two characters really matters, as in Season 2 Will hardly has a stroyline that isnt tied to him needing to be saved. Though the major points include: Lucas being gentle with Max and sneaking her out when he knows Billy will get mad, talking her through the risks of knowing everything, standing up to billy, and not rubbing it in Dustins face when he and Max do get together. (Though thats a weaker point) Will gets some points for being okay with Max tagging along and the CloseGate thing.
Season 3 Will spends his time wanting to play DND with his friends, much to their annoyance. For the most part thats fine, but its when El dumps Mike that we see Wills priorities. He does not care even a little bit, nor does he try to empathize for a split second, going immediately into "can we play dnd now?" Will also hardly cares about Dustins radio or the fact Suzie didnt call. At dustins disappointment he leaves and says "maybe tomorrow we can play dnd or something fun". Yes Lucas leaves aswell but he doesnt make it about himself or what he wants to do.
Lucas however, talks Mike through the breakup and tries to help him get El back. When Will forces them to play DnD he complies along with Mike until they call the girls. While Mike biked to Wills house, Lucas is the only one that follows up and actually apologizes for the whole situation. What does Will do? Takes no accountability for the fact that he couldve at least tried to be a bit more understanding.
In Season 4 Lucas takes full responsibility for him and Max's breakup, stating he should've looked harder. He also calmly and carefully explains to fhe boys why the basketball game means so much to him. Then later, when he realizes the team is about to hunt down Eddie, Lucas immediately rushes to their aid. And of course he goes with Max and protects her from Jason.
This contrasts Will in Season 4. He does not stand up for El, nor does he try to understand anything from her side. Then during Will and Mikes argument Will puts all the blame onto Mike for not reaching out. He then let's Mike take the brunt of the blame for their fight and their distance, though they are equally at fault.
Season 5 they stop being super comparable because their personal stroylines are too contrasting. Lucas stays by Maxs bedside and helps with the upside down stuff, while Wills arc is mostly about accepting himself with very limited interactions outside of Joyce and Robin.