[Perfectlap]

Thor was not the best choice but I give him credit for losing 100 pounds to play Hunt.
I think Jude Law would have been a better choice for pompous and "posh" racing driver.

And I would have given Cristoph Waltz a shot at playing Lauda. But at the end of the day these racing films never do well because racing drivers with a couple of exceptions like Senna, aren't that interesting in real life. It has to be an interesting story first, which you certainly had here, but the script has to be very gritty and raw. This was more a PG-13 type of a thing. You could only do so much with this script no matter the casting.
Downton Abbey has more interesting script-writing and that's about a bunch of rich unemployed people eating dinner in tails every night.