By my count, there are currently 17 stories from Kaladesh block. Yahenni, Rashmi, Pia and Dovin each had two stories told from their perspective. Kari Zev has one from hers. That's about half of the stories from non-Gatewatch members (slightly more if you want to count Ajani's story).
The bigger problem, I think, is that the non-Gatewatch stuff tends to not make it onto the cards. That might be an issue of lead times though. They might just have the major story beats down when commissioning art and focus on the minor scenes too late to make putting them on cards viable.
I have a rule with movies/TV/Games- if there is lore that is in a tie-in comic book but not actually in the actual Movie/TV/Game, it's nothing but glorified fanfiction to me. I don't read the Magic Story, I play the actual cards. Maro talks about "if something isn't at common, it's not a theme in your set". If something isn't actually on the cards, it's not something I care about. I'm sure Yahenni is a cool character and all, but he's on like 3 cards, while fucking Ajani is on at least 2 cards in any booster you open.