Literally the only way that you can like Mike Wheeler in s4 is to believe that he’s suffering some kind of sexuality crisis/is falling out of love with El, some other major secret that we don’t know ab is affecting him, or that something major is going to happen with the plot. 

In S1, mike and el were almost like the two leads (and definitely the main characters of the younger kids), with el driving the plot forward bc of her powers/connections and mike driving the plot forward emotionally with his relationships/emotions etc. In S2 this is continued (albeit a little more blurred as Mike gets involved more with the lab and El strikes out bc of her feelings/relationship with Hopper and Mike) but ultimately those two are still the ‘core’ of the show, emotionally or otherwise. In S3, the two are finally actually together (unlike in S1 when they didn’t know each other that well), and thus the rest of the characters get more time to shine (Dustin especially as will also had importance in S2). Even though Mike and El take a backseat in being the most ‘connected’ to the lab/to the other characters, they still are important, especially in the party. 

And in S4, el is still hugely important to the plot/tied to the lab, but for the first time ever Mike is NOT the heart of the show. This had been leading up since s3, when Mike was too wrapped up in El to focus entirely on the other people, but this is the first time we’ve seen mike really suffer emotionally/ be the ‘bad guy’ in a relationship outside of his relationship with el. To have this drastic character shift from someone who was the heart of the show(/the party) to just this asshole (aka regular teenage boy) means that something major is going down — either with him, or with the show. 

In show the duffer brothers chalked up this major character shift to mike not being ready to say ily; assumed to be bc of his parent’s relationship, but not explicitly stated. If this is the case, then I’d hope that they address it more explicitly in S5, especially bc it seems that Karen (and holly?) are going to be more important. If this is the case, then it means that the entirety of Mike + el’s relationship has been built on a loose foundation, and so s5 might reflect s1 (like the duffer’s said) in terms of el and mike ‘restarting’ their relationship. It would also make sense that Mike is finally starting to really show the signs of his family dynamic at home as he goes through puberty and changes etc.

AND, if this shift is also a reflection of the show, which I believe it should be, then I think that we should be maybe more happy about s5? Mike has always been the emotional core of the show in some capacity, so the fact that he was in turmoil in s4 reflected how jancy and Lumax, the only other two well-established ‘long term’ ships in the show (except for maybe jopper) were also having relationship issues (also seen in s3). Now that mike’s thing has been semi-resolved, hopefully that means that there won’t be too many relationship issues in s5??

It can also be seen as the other way around, in that mike’s inner turmoil is only reflecting the way relationships will continue to fraction as the action ramps up in s5, to the point where even the emotional core of the show isn’t as empathic and kind as he used to be

(If it’s because of a sexuality crisis (which I really doubt will be the case in canon but idk), then the ily thing hits even harder and the comp het etc etc is self explanatory— and if it continues in s5 (esp in terms of mike/will), then it could be a reflection of s1 w mike ‘finding’ will in a new light?)