Source: Supergirl (2015- )
I know the casting and portrayal has been rejected in some quarters. Not overtly because Brooks is a black actor and the "iconic version" of the character a ginger, but because he's buff, and a heartthrob, and too much of a presence to ever be the nerdy "pal" getting his bacon saved consistently by Superman. I couldn't disagree more with that assessment. Here's my unreserved defense of Brooks as Jimmy, and it has nothing to do with the diversity issue.
The common complaint is that if the portrayal is going to be completely unlike the iconic comic book version, then it should have been an entirely new character. But is Brooks' James Olsen "unlike" the comic book Jimmy? I don't think so. (I do feel that way about Supergirl's version of Vartox, however.) If your problem is that Jimmy can't possibly be popular with the ladies and an action man, then I will point in the direction of the Silver and Bronze Age Jimmy Olsens. Hell, even the post-Crisis Jimmy had a prolonged affair with Cat Grant!
Perhaps you can't imagine a guy in a bow tie as a heroic sex symbol (but aren't we past that in the post-Matt Smith era?), but the comics didn't. Jimmy was a "nerd" in various films and TV/cartoon shows, mostly based on what modern audiences think of his look. In his prime, he had his own fan club separate from Superman's (we're talking IN-universe now), had his own book in which he had many daring adventures (including Jack Kirby badassery in the Fourth World), and even called himself "Action Man". Alien queens would come and ask his hand in marriage, and though Lucy was harder to get, she always came back calling. So in the books, he WAS an action-oriented hero, and DID have luck with the ladies. All they really did there was update his look to something less old-fashioned. Jimmy became a total nerd BECAUSE he was still dressing the way he had in the 50s when that getup was still cool.
As it is for Superman, so it is for Lucy. Just like in the comics, she's got him wrapped around her little finger. No matter who studly, SHE runs the show, SHE decides if they're together or on a break. And he has very little say in the matter. That's Silver Age Jimmy in a nutshell. All complaints that he's too handsome fall apart because he doesn't ACT like the handsome one.
And then there's the fact that this isn't a Superman story. Jimmy has always been rather malleable when not paired up with the Man of Steel - in his own adventures, principally - and he doesn't fill the "Jimmy" role in Supergirl's life (Winn is closer to it). He's part of a romantic triangle, he's a bit of a mentor as Superman's ambassador, and he's a friend and confidant. They've allowed him to grow up. They asked, where would Jimmy be in his life a few years down the road, if he were actually allowed to change? And what if we then put that guy with Supergirl? Jimmy as mentor figure? That's flipping the tables on the Jimmy-Superman relationship, which is really interesting.
And Brooks is a very good actor. Bottom line, that's what I'd rather have than a comic book look-alike. That scene where he talks about the first picture he ever took is one of my favorites of the entire series to date, and the best "secret origin" for Jimmy I've ever seen. And since you've cast a black actor, use it. His line in the anger management episode about knowing all about the importance of not showing your anger in public added layers to the character.
I don't know about you, but I think they're giving us the perfect blend of the character as we knew him, the character as he might be in new circumstances, and a little bit of something new.
Now, that doesn't mean I wouldn't welcome a bit of Elastic Lad or Turtle Boy...