I'm no expert, either, but I wonder if the reason Caroline does better in the off-season, at least as far as the rumors go that her jumps look improved, is because she is able to work on each jump alone, then once she puts them into a program, especially when in competition where nerves surface, muscle memory kicks in, and the old habits resurface.
As far as the Mirai comparison-IMO, Mirai has always had the better foundation and basic skills, even as a Jr. skater. She always had speed and bigger jumps. Yes, she always had a flutz and Frank is working to have her relearn her technique there (especially if they keep going for the 3z/3t) and I think her URs came with growth spurt/injuries, because her jumps looked better in 2006-08. Whereas, Caroline has always had suspect issues on her jumps, especially the 2ax, 3fl, and 3lz, and lacks speed/power to her skating. They are pretty even in spins, but I'd give the edge to Mirai for spirals and footwork (due to better speed and edges) . I think when Mirai felt more pressured at Worlds, she reverted back to her UR habits, basically relying on muscle memory to get through the LP. But the fact she was so on fire AND clean at Vancouver shows she's made big improvements to her jumps and presentation skills (IMO).
As far as the Sasha comparison goes-again IMO, I think they have very similar strengths and weaknesses, but Caroline's weakness are much more glaringly obvious. They both lack power, speed and deep edge work (Sasha HAS come a long way starting around 2005, I think, when she began to focus on those aspects). Both tend to wobble on their edges into toe jumps and have a high toe pick. Sasha has a much better 2ax though. Their strengths are their flexibility, the fact they can hit beautiful positions, have wonderful upper body carriage and amazing spinning ability. I've always felt both were more introverted skaters, although Sasha did a great job with her SP choices, just felt she never carried that same attitude/personality over to her LPs. Caroline seems to be the better mentally tougher competitor, she has shown when she is confident, she can keep her nerves in check and stay upright. I believe if she can fix her jumps, gain more speed/power, her confidence would be much higher and she'd deliver 7 triple LPs more often.
Actually, between Mirai and Caroline, I worry Mirai could take the same path as Sasha-deliver amazing SPs and succumb to pressure for the LPs. I really hope Frank works on this with Mirai. Part of me believes if she gets past her URs issues, no matter how nervous she may get, she'll be able to rely on her training and muscle memory to pull her through. Because of reports that Sasha wouldn't work on her weaknesses or do run-throughs, I always believed she lacked mental and physical preparation, so she would lose confidence as she tired, because she didn't have the muscle memory to fall back on.