Which explanations do you think would be more lore-driven than theme-driven? I suppose reference to Imperial remnants might be lore-driven, but I’d also argue that it could work thematically as well.
If the death of the Emperor, their undisputed figurehead, was kept the Imperial remnants from reuniting, the idea that Kylo Ren, the heir apparent to Darth Vader, could have been used as a new symbol to reunite them is an interesting idea that ties into the theme of unity and power that I mentioned previously, and it could make Kylo Ren the symbolic antithesis to what Luke represents for the Resistance/Republic.
To me, I think it is about finding a nice explanation that feels satisfying and is a believable progression of the story from ROTJ.
It seems like the two biggest questions regarding the political situation are:
How did the First Order get the resources to build a new military without the New Republic doing anything about it?
What is the purpose of the Resistance, and why isn’t the Republic doing anything about the First Order?
These two things, without proper explanation, is what makes a lot of people feel we are back at Rebels vs Empire again. At face value, the bad guys just have new ships, a new army, and a new super weapon, and the good guys are still scrappy underdogs.
Like you were saying, maybe a good idea would be to rewatch The Force Awakens (theatrical or Restructured) and completely ignore the opening crawl, then based off the facts the film itself gives, try to determine what the most accurate explanation would be based off what we are given within the film.