I think that's exactly why Chuck screwed over Jimmy. It's jealousy. I think Chuck realizes that Jimmy might start outdoing him in the field, especially with this electromagnetic OCD mental illness he has. Remember Chuck's reaction to Jimmy passing the bar exam? Looking back, you could tell he was shocked. In Chuck's mind, his baby brother is still a **** up. He doesn't want to believe that Jimmy might be at his level as an equal. That's why he doesn't want him to be a partner. He wants Jimmy to stay in the mail room.
Hell, Jimmy figured out the fraud at the nursing home as soon as he looked into it. Chuck had already gone over all those files when he did the wills and missed them. Jimmy caught something that Chuck missed, and it is something big enough to where he could have demanded anything he wanted from any law firm. To me, this is a matter of jealousy. Chuck is pissed that Jimmy, his silver tongued, scamming little bro, managed to 1-up him. Before Jimmy reformed, he always had to rely on Chuck's help. Chuck was essentially the person that bailed Jimmy out. Now, it's the exact opposite. Chuck is the dysfunctional one relying on his brother and Jimmy might just turn out to be better at something that Chuck worked his whole life trying to attain. The "LAW" and "INTEGRITY" BS Chuck is spewing is a front.