The revelation last night really put a huge spin on things -- and you could probably sense it coming, but now it's completely out in the open whereas before it was swimming murkily under cloudy water and all you could see was the tip of the fin.
Hamlin -- while he doesn't much like Jimmy -- hasn't even really been the problem even if Jimmy views him as Satan and his ultimate nemesis and Hamlin actually doesn't much like Jimmy. In terms of Jimmy's future at HHM, Hamlin's just been the puppet whose strings ultimately have been pulled... by Chuck. Yes, big brother Chuck has been driving Jimmy's dashed prospects at the lawfirm that even shares a piece of his name, THEIR name.
Chuck, who has a certain view of his little brother and can't get past it because it will shake him up at a time in his life when he himself is struggling with certain mental infirmities. For Jimmy to succeed means that Chuck is "less than" he though, and so Jimmy must never succeed... must never be taken seriously.
I think what makes it devastating is that it's clear that on some level Chuck does love Jimmy, they ARE brothers; at the same time, there's a lot of resentment, disgust, and non-acceptance of Jimmy as a human being that Chuck hasn't shaken and seems unwilling to. And... while Jimmy is being viewed as "less than," a lawyer who is like a "chimpanzee with a machine gun," what we the audience have seen is that Jimmy is a better man than Chuck. This guy who ends up a "CRIMINAL laywer" (versus a criminal's lawyer) in BB actually has quite a heart, and it's clear he loves and idolizes his older brother and has worlds of patience and respect for him. Jimmy adores Chuck, and so much of his behavior is driven both by a need to get his brother's approval as well as his actual affection, especially in a time when Chuch has been brough so low and isolated by his illness.
Do we see Hamlin and Associates come by to visit Chuck? No. Anyone in general? No. It's Jimmy. Jimmy who brings him his food, his news, human companionship, who has tolerated his crazy bullshit illness and psychotic behavior, who is SO very patient with him and slowly tries to coax him out of the literal darkness, who doesn't give up on Chuck. It's been Jimmy, and it's not something we got to see nearly as much in BB although often the way that Saul would intervene between Jesse and Walt suggests he actually does have a heart; Saul was never ruthless, he just was a dodger and huckster. He never wanted to hurt anyone.
Anyway, here we see the tender side of Jimmy -- he loved his brother and could tolerate almost anything (which kind of explains how Walt was so easily able to victimize him at times) -- and so it is absolutely devasting when we along with Jimmy finally come to realization that the one person Jimmy adores and has given so much to and whose respect he desires is the one person who will never ever give it, simply because he's selfish and cowardly.
So now it all makes sense. Hamlin is angry because he wants the damn case, but Chuck won't let him take Jimmy on in order to get it; so then he is treating everyone like shit because he's frustrated that Chuck is complicating things and also because he's stuck playing the "heavy" because Chuck never had the balls to just do it himself. Meanwhile, Kim really is Jimmy's friend and proves it here -- she encourages to do what is best for him in the long run, while not wanting to break his heart by telling him about Chuck's duplicity. "Just take the money, Jimmy." Even after Jimmy says some pretty nasty stuff to her, she sticks to her guns... because she knows Jimmy is just upset, doesn't mean it in the end (she's right -- he spends all night thinking about what she said, until he figures it out), and because she wants him to get through this with the money and his dignity intact.
It's pretty clear that this is a hugely decisive moment for Jimmy and has huge ramifications. It makes sense that he would change his name -- he will want nothing to do with Chuck, while "punishing himself" at the same time by taking away the name he doesn't apparently 'deserve". And much of his "going good" was to please Chuck, to make him happy; since Chuck thinks so little of him, there's no reason to try anymore and meanwhile he's just again becoming what Chuck expects of him, he's still Chuck's thrall in a sense.
I found myself really angry watching that last five minutes, as well as devastated for Jimmy. He was so angry and so heartbroken at once, and Chuck wasn't just being a coward -- he wasn't even being rationally fair. Regardless of the school Jimmy attended, he passed the bar. On his own. He failed twice, but many do; but in the end, he actually passed the test, so regardless of the school he still knows his law and thus has been judged competent. And he's a street-smart lawyer, not a hack; maybe his formal case style sucks, but he's willing to get down and dirty and do what it takes to win... the poor down-on-his-luck Irish scrapper who might be smaller than the other kids, but never ever gives up.
Chuck's an ass. He despised a brother who has cared for him when everyone else gave up on him, and instead of supporting him, he kicked his feet out from under him when Jimmy tried to "do right" and be more than who he was. What a dick.
I think it also highlights the Walt/Jimmy difference again. Walt was someone who looked good on the surface but had some rot in his heart, and he doesn't quail at inflicting violence (physical or emotional) on others as his outer and inner start to align.
Jimmy looked shady on the surface but always had a good heart, but getting kicked around by the people / things that mattered most to him dragged his expectations for himself down to the dirt. He's still a good guy under all the mud, though. Which is why he is likeable.