A lot has been said about how the show dramatically whitewashes Tyrion’s character, morally speaking, compared to how he is in the books. I’ve thought about it a lot myself. I think I saw it summed up best on one of the Westeros.org forums. After Ned was executed in Season 1, the showrunners set Tyrion up as the hero of the story, the “good guy” that viewers could root for. It’s a contrast to how morally gray he is in the books. A lot of people have debated whether this whitewashing of Tyrion is a good or bad thing.
I think I’ve finally made a decision. Yes, his portrayal in the show is a departure from his character in the books. He’s definitely more noble and good. However. It is revolutionary, it is groundbreaking, to see a disabled man, a man with dwarfism, portrayed as one of the heroes of a whole goddamn fantasy epic. I feel like Tyrion in the show, especially in his trial scene in Season 4, has also powerfully called viewers’ attention to ableism. His father and sister, especially his father, hated him because of his dwarfism and the fact that he was different. He called them out for it and that was too powerful to be ignored.
The showrunners have made a ton of ill-advised and flat out bizarre decisions, but for the above reasons, I think portraying Tyrion as one of the heroic characters of Westeros is not one of them.