The focus on Ghost Rider worked because he was needed, and as Jeffrey Bell said to TVLine, he might feel like a bit much if he hangs around full time after the Eli Morrow arc.
Besides, Ghost Rider is known as the “Spirit of Vengeance,” not the “Spirit of Status Quo,” and the death of Eli Morrow meant the satisfaction of his quest for revenge.
Ghost Rider’s presence on Agents of S.H.I.E.L.D. Season 4 had been necessary due to S.H.I.E.L.D.’s conflict with antagonist Eli Morrow, so the comic anti-hero didn’t feel like he was taking over the narrative from existing characters during his arc.
Sure, Robbie may have gotten more time on screen than Fitz or Simmons, but neither Fitz nor Simmons have abilities gained from selling their souls to the devil.