I think in honor of my post that partially complained about the lack of Rex's backstory having a tangible effect on how Rex interacts with the GDA/Cecil in the show.
I present to you a small list of things I personally would have liked to have seen and a lot of this revolves around the need for Rex to be like 1000x more skeptical of the GDA. And this doesn't even have to mean gigantic structural changes to the shows story.
Things of note before hand:
A) Rex was originally fully down to murder Cecil, before he learned that there were going to be additional collateral in the form of the entire pentagon staff.
Rex was roughly told that "the GDA is no longer on the side of the US government and Cecil has gone completely rouge"
B) Rex has been informed that Cecil is Radcliffe's hand-picked protege.
Now if I were Rex my first question is "why does my dad want this guy dead?" Then my second question would be after the whole fiasco, "Did I make the right choice sparing this guy?"
And I think that would eat him. Like what if his dad was right? But also important in my opinion, what if Cecil is exactly like his dad...(he was his protege after all).
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I think Rex should be against Robot accepting the job of working exclusively for Cecil to form the new guardians of the globe.
I think he would want to remain independent. However Rex will be summarily outvoted, as he is unwilling to divulge his backstory to properly explain why, other than Cecil has "bad vibes".
Rex just can't up and leave the team to strike out solo, my man has exactly 0 connections, no legal documents, or alternative housing probably. So he is forced to go along to the tryouts.
2. Rex's introduction to the other members of the new Guardians of the globe should have gone differently, specifically Amanda and Sampson
Like Rex was recruited probably around the age Amanda appears to be. To deliver a naive kid into potentially the same situation he had with Radcliffe? He can still be a jerk about it, but I think it would sound a bit different than it does in the show.
Being rebellious with Sampson, this is Cecil's old guard of course he is uncomfortable. I think the jabs should be more aimed not fitting in, being old, and stuff, not the lack of powers.
3. I think Rex should initially/ in the first season look uncomfortable/on edge in any GDA location Especially any time Cecil and Rex are in the same room or he is on screen.
Rex is not dumb, so I don't think he would be outright combative against anything Cecil ever does or says, more like on guard waiting for the other shoe to drop, for the mask to drop just like Radcliffe. It is perfectly reasonable for him though to grow more comfortable and display it less often as the series progresses and he grows more comfortable. However I do think it should return when Mark starts getting belligerent with Cecil (reminiscent of how it went down hill when Rex defied Radcliffe's orders)
4. I think Rex should have been the one to lead the discussion on leaving the GoG, like in the show its Amanda and Ray talking about how Cecil uses them, doesn't care about them and sees them as weapons.
HELLO?!?! Rex is right there?!?! Mr. I have very personal experience with this except phenomena? This Cecil's true colors moment, just like Radcliffe. Why is Rex staying silent until one of the ladies speaks up??!?
*also side note, I don't think Rex should have stuck around to clean up, I think he would quit on the spot