I certainly think it is a giant issue. I think that entire story completely fell flat to me, and I think they ruined his character in the process. But in a simple who's to blame, it's him over Dern's character without question. I'm not saying I don't also think it was just a very bad decision to have the scenario take place at all.You don't see that as an issue? This is one of the things that people are complaining about. In order for his character arcs to work, Rian Johnson twisted already established characters and shoehorned them into situations that didn't make sense because he couldn't make the movie work otherwise.
It's funny with this film, because it feels like two films, and one of them I mostly like, and one I hate. We can call them Rebellion/First Order and Jedi/Sith halves. Other than a few poor uses of humour, and the utter stupidity of Snoke not being able to read Ren's coup plot, I love that half of the film. I think it works incredibly well, I love the way Luke went out, I love how Ren breaks Rey's heart when she thinks she's turned him for him to just completely pull the rung out from under her and assume command himself. A lot of the issues people have with that half of the film, I don't have at all, I thought it was sublime.
The Rebellion/First Order half however... I hate it. I hate Poe's mutiny, it's fucking stupid. I hate the 'chase'. I hate casino world. None of it worked for me. The hyperspace ramming is visually remarkable, but it completely tarnishes every other assault in the history of the series.
I thought it was really weak. TFA is extremely safe, but I still enjoyed it more or less from start to finish.