I didnt love S3 but Steve peaked there. Robin became the final puzzle piece he needed to complete his development - thanks to the actors because the duffers clearly didn't know what to do with him. Steve spent the last three seasons chasing after a girl who would never be his soulmate, and when he accepted that, he tried to find someone else to love instead. He tried flirting with any girl whose attention he could hold for over 60 seconds, except for Robin - setting her apart already, though for the wrong reasons initially. She was originally meant to be Nancy's replacement as Steve's arm candy, it seems, but making her a lesbian at the last moment is really what saves S3 for me, not only because she's my baby, my favorite character and I adore her with my whole heart, but also because... the improvised straightbait turned out to work incredibly well at the time to cement the conclusion of Steve's arc - he was a piece of shit and lost Nancy to someone who was better for her (say what you want about Jonathan, but that's clearly the idea the writers had with him, regardless of the effectiveness of the execution). Steve couldn't get Nancy back, and really, he shouldn't be focusing on romance at all because that's just not what he needs to grow as a person. The people who truly challenge him, push him to be better and motivate him to grow are his platonic bonds - Dustin and Robin. He couldn't "fix" everything with Nancy (meaning that he couldn't go back to before everything changed, as if he hadn't messed up). Nancy may appreciate the change but she won't go back to him. Steve doesn't need to change for love - he needs to change for himself, in order to be a better person, period. And Nancy has no reason to stay and watch him grow, she has her own matters to attend to, and she doesn't have enough space in her life for Steve. So Steve finds new people, somewhere else, away from Nancy, and he grows thanks to them.

Robin being not only just his friend but also being completely and eternally unavailable to him works perfectly here. The audience believed, alongside Steve (and the Duffers lmfao) that what Steve needed was romantic love, but Robin proves him wrong. He gets over his ex-girlfriend and finds a sister instead.

And then Season 4 ruins that, for no reason and to no one's benefit. Steve regresses. The growth is undone, for the purpose of keeping Nancy in that eternal love triangle loop that seemed to have been solved two seasons ago. It's sad and disappointing and I'm hoping they don't revisit that in S5.

What I would've done instead would've been to let Steve finish his arc in S3. S4 Steve has a flat arc now. He learned all he had to learn. He's fine. Now, he's here to teach others what he's learned, and I think it would be very interesting if the person who learned from him the most turned out to be Nancy. Steve basically just discovered the power of friendship, and deep emotional connections and trust and how closeness to others makes you stronger. Gives you a purpose. He learned to love and care for others and now that's his strength. Have him tell her about how much he cares about Robin and Dustin. Show him bonding more with Lucas and Max. Contrast him with Nancy, who is isolated, who just lost another friend after leaving him alone, and is desperately trying to protect Max from Vecna. Maybe she's hesitant to become friends with Robin, or to rely on her and Steve to share the burden, or trust the kids to take care of themselves on some capacity. Nancy has become more and more isolated as Steve grows closee to other people.

Then Steve sacrifices himself in S5 to save either Robin or Dustin or both of them idk I think that would be the best conclusion to his arc. Passing on the torch to one of them. Maybe Robin becomes the new babysitter and protector. Maybe Dustin becomes the new hot boy at Hawkins High idk but I think an ending of this sort would fit. He doesn't even need to actually die, if he somehow survives it still works, just having a sacrifice scene (not played for laughs) would be a perfect way to conclude his growth and move on to inspire others to grow like others have done for him.