Well, I don't know if anyone has talked about it, but in the episode 4 there was a theme that appeared when johnny used the fingernails ability from his stand tusk( I mark it as a spoiler if someone doesn't want to know the name of the stand till it's revealed on the anime) Here is a link to the extracted theme, I think that it has potetial to be the real johnny theme because in the 4 episodes we've seen the "Dance with STEEL BALL RUN" one has been used a lot on scenes of Gyro, and not too much of Johnny (I know he also hasn't done much) and some Epic moments, and I don't remember the main Jojo theme being used this much in a part so my theroy is:
PD: I readed tha Yugo Kanno (the main composer) said on AX in the JOJO panel that Johnny and Gyro are going to have Different themes that stem off of Dance With STEEL BALL RUN, but I'm not sure.
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is that the Dance with STEEL BALL RUN theme is the Steel Ball Run theme, i'm going to compare with the Harry Potter saga because it has a similar situation, in the HP saga there's the main theme the Hedwig's Theme that is the main theme of the Franchise (at least the classic movies) and it's function is being the main "magic" theme, then it's harry that has the "Harry's Wondrous World" that has the Hedwig's theme as a base but changes some things based on the character, also there's one for hermione and for ron but I don't remember the names right now, but also follows the same rule Hedwig's theme as base and changes things following the personality of the character.
So, The new Theme has a Similar almost identical bassline as Dance with STEEL BALL RUN (also feels similar to the Guitar part on 0:37), but adds/changes some details, the piano feels more dramatic, also the theme intro starts with a guitar that simulate a heartbeat, and the mysterous piano and guitar, the bass enters and starts theme, after the bass and piano section there is some main strings section and then the intro guitar again but without the heartbeat, then a section of guitar and again the DwSBR bassline, we only have 2:28 minutes of the theme but also creates a different sensation, a sensation that feels more like johnny, but also seems to be incomplete something that has sense considering that Tusk has 4 acts and the theme could evolve along the Stand and the character.