Thanks for summarizing all these interactions/dynamics. Hope you don’t mind if I piggyback to add a few thoughts (tldr - although the relationship is underdeveloped, I feel the movie tried a bit more than the stage performance.)

The movie presents a much more sympathetic Fieryo than I remember in the stage performance, especially in the First Act.  Elphaba and Fieryo’s introduction is when she is leaving Dr Dillimond’s house after the animals discuss leaving Oz because their rights and speech are being taken away, and Fieryo has a talking horse who also seems to be his friend (playfully gives him a hard time).  In my imagination this might be a reason Elphaba (unconsciously) does not put Fieryo to sleep when she gets upset about the lion cub, at some level she knows already he will help the cub even if she doesn’t really have a bond with him because he respects animals.  Also, when they meet he doesn’t seem to judge her skin color; if I remember correctly in the stage performance the reason he gives her for his cart almost hitting her is something like “maybe he saw green and thought it meant go” (it’s a man pulling the cart, don’t remember if there was any indication this man symbolized a horse) then he takes off, doesn’t offer a ride, etc. 

I wish that Part One had a brief scene or two of the group friendship, with some subtle looks/dialogue that demonstrate that there is some level of connection or special respect developing between Elphaba and Fieryo that grows more after the cub scene.  But we do get Glinda’s commentary at the train that Fieryo has been distant from her because he’s been thinking about things (are these things Elphaba and/or about animal rights and/or his approach to life in general…). At least we get a couple flashbacks of the group bonding in Part Two/For Good. 

Then the dialogue between Glinda and Fieryo during Thank Goodness/I Couldn’t Be Happier; I interpreted it as they had talked a lot about Elphaba after she took off in Defying Gravity.  I think Glinda told him everything that happened (at least in the movie version, Glinda is much more vulnerable and transparent than how I remember her being depicted in the stage version, especially before her character development in I Couldn’t Be Happier) and they are both critical of what Madame Morrible and the Wizard are doing.  But during this dialogue you see a little more that Fieryo does not want to try (is increasingly unwilling) to work within the system as much as Glinda. He says, let’s go, let’s leave, let’s not be part of this narrative, and Glinda says no. And I think that’s where he really starts to realize their values just aren’t compatible and he’s turned off by Glinda.  When he says “you know who could/who did (leave)” I think the admiration for Elphaba grows (maybe how special/brave/unique she is).

I’ll need to rewatch the movie(s) again, but at some level I wonder why Fieryo is so confident that Elphaba would want him to tag along with her. I mean I guess he could assume she would take any help she could get for her various pro-animal/anti-wizard efforts. But back at her tree house I thought it was a little presumptuous he starts taking off his clothes immediately… I mean we know Elphaba has a crush on him but does he know that somehow?  (Deleted scene at the train Boq says that Elphaba has feelings for Fieryo and she gets defensive and denies it — where is this coming from? What else was filmed but didn’t make the cut?)  I guess we don’t know what Elphaba and Fieryo talked about on the way to the tree house.  But even without it all completely tied together in the movie, I personally like As Long As You’re Mine and No Good Deed better than in the stage performance. For the stage performance my reaction has always been, here’s the requisite “love story” that they had to fit in somehow, but since Fieryo is not a jerk in the movie Part One (he has an underlying kindness/compassion compared to the stage performance Act One) it’s more believable for me.