It may be a language thing, but, to me the phrase "too historical" suggests that the movie stuck too closely to the facts for your liking. Whereas, for me it strayed too far from them.
Yes, a good enough good job, Whether it deserved an Oscar, I don't think so. As mentioned previously, I think that Simon Russel Beale gave a far more convincing performance in Aunty Beeb's "Dunkirk". And lets not forget Albert Finney's "Churchill" and Vanessa Redgrave's "Clemmie" in The Gathering Storm, probably the definitive portrayals of both of them. Even the toilet scene smacks of a rip off of the bath scene in The Gathering Storm.