Yes, because by season 4, Steve has more importance than Jonathan.

I mean I guess

Depends on season.

S1- No, S2- Maybe, S3- Maybe yes, S4- Yes, S5- Both can be somewhere.

Does it really matter. Both are good actors just Steve's character is developing and Jonathan's character is dissolving. Hope both characters get along in S5.

Yeah, they're great actors, but the opening credits are listed in accordance to the character's importance.

As presidentesmith said, it depends on the season.

Joe Keery "Steve Harington"

S1: No, although Steve isn't that bad and has development since the end of this season. (Joe in this season was not in the credits and he was not in the official poster either)

S2: probably

S3: Yes definitely

S4: Yes, absolutely

S5: Of course

The two actors are amazing, kind and cute, this has nothing to do with them and real life, but if we talk about character development and importance

Steve is better than Jonathan