In my opinion, both character arcs were done poorly. As you said, Supreme Strange going backwards after already coming to terms with Christine's death felt unfulfilling. As for Wanda, I think her turning evil makes sense, but the problem is it was all done off screen, which robbed Wandavision of a lot of meaning.

I think it would be good if Wanda returned but I do think that her arc was not as bad, I hope the Agatha series can tell us more about her becoming evil and maybe let us see the beginnings of it

Wanda Vision has a post credit scene that explains how Wanda got corrupted by the Darkhold

Doesn't give enough context. We still need to see it happening.

I mean while they are similar I found Supreme Strange’s story more interesting that made him work as a villain

While I love Scarlet Witch I just didn’t see her work as a villain

Strange Supreme's Heel Turn comes out of freaking nowhere and was a complete betrayal of his character and this is coming from a guy that was a massive fan of his during the First season.

Wanda's arc meanwhile make sense because what she was dealing with at the time with the Darkhold and her character. Wanda's Character is someone that would have been corrupted easier and we did saw that corruption during Wandavison when she start reading the Blasted Book, The Darkhold corruption isn't something that happen over time, it's has always been sudden ever since it was first introduce in Agents of SHIELD. It's make perfect sense in the world for her to be easily suave by the book espeically if it's involves the only family members she got left in this world in her Kids. S. Strange, Meanwhile could easily move to another universe with a Dead Strange and a alive Christine instead of turning back to the dark side once again.