You kinda have to ignore the context of things in the new movie and the headspace Finn was in in the last movie to say that him not being super eager to join up isn't a valid avenue to explore for his character.
consider the following:
By the same token, we did not need Empire Strikes Back to be a story about Han accepting that the Rebellion's cause is worthy; separating him from the rest of the cast to be berated by some rebel leader about the ins and outs of the war and why he should become a selfless general.
No, when Empire starts, Han is a general.
We don't know what motivated Han to come back at the end of ANH. Did he want to save Luke, because that plucky duck reminded him of a young Han telling the Empire his name is "Solo"? Did he have a thing for Leia? Or did he fully devote himself to the Rebel cause? We can all have our theories, but the way the saga plays out, it would seem all three are correct.
Finn is practically in the same boat. Uncertain allegiances throughout TFA culminate in him taking a heroic stand, one that is mostly encouraged by, you guessed it, Han Solo. (It's like poetry, it rhymes!). Revisiting Finn's allegiances in TLJ is just as awkward as doing the same for Han would have been. TFA is a retread of ANH, and Finn is Han Solo
The authors of ESB mined the content of ANH to find the most interesting plot threads to carry forward. What is interesting about Han Solo? Is it that he isn't fully committed to the Rebellion? Or is it that he's wanted by bounty hunters and even name drops an intergalactic space gangster? Is it that he needs to learn to fit into the rank and file of an established command structure? Or is it that his vagrant past has likely left untold friends, enemies, and everything between in it's wake? Which story would be most interesting to follow up on???
Do the above analysis for Finn, and see if you can think of something, anything about Finn as presented in TFA that would be more interesting than re-affirming his allegiance to the rebellion. It's not a tough exercise
Also, if TLJ had been written
any other way, dollars-to-donuts you would not be in this thread with the following hot take:
"You know what? It was great an all that they had Finn <choose one of the following>:
A: infiltrate FO recruitment and de-program his fellow former troopers to the Rebel cause,
B: clandestinely follow Rey to Ahch-To, discovering the location through shear will to reunite with her, only to discover an affinity for training with Luke (regardless of whether or not he's actually force sensitive)
C: get chased down by Phasma for being a deserter, resulting in a climactic final showdown that elevates both characters to prominent status going into the third movie and gets the attention of both the FO and the Rebellion
D: do literally anything else that actually builds on what we know of Finn from TFA in some meaningful way, those were just the three that immediately jumped to mind, they are not my "fan-fictions", they are some of many possible extensions of where TFA had Finn heading
but you know what really would have made this movie better, is if instead of doing the above, we got to see Finn learn to devote himself to the rebellion, you know, because it was kind of unclear exactly what his motivation was when he took that stand at the end of TFA... That's what I would've liked to see. I'd have liked to see Finn learn about the ills of arms of trading, not by actively thwarting some form of arms trading, but by being told about how bad it is, while hunting for a McGuffin that he would know about as a former FO member, while being lectured about why he should respect the rebellion more than he already seems to along the way. That's what this movie is missing"
Have you ever had that above thought about Han in ESB?
No, you would not be saying the above
Neither would John Boyega
Nobody would
I get it, you liked the movie and you want to defend it. There are things to like about the movie, and there are things worth defending. It's not my place to tell you you shouldn't like the movie.
But it's easy to see that there were more natural and interesting directions to take Finn's character. You can still like what they ended up doing, but I suspect there are plenty of alternate solutions you'd have liked just as much (or possibly more)
