I think the problem is obvious. You’ll notice Trevorrow and Connelly are credited for story. With the drastically short schedule, Abrams essentially had no choice but to inherit much of Trevorrow’s story (because of preproduction work that had already been put in, without enough time to start from scratch). But Trevorrow’s story was broken enough to get him fired, so…
Also, Hamill is definitely wearing a wig (except for when he lifts the X-wing, which I assume Rian shot for Trevorrow).