The railroad construction was amateurish and not realistic. We never see the organiziation that went into the speed construction records. A few times we are treated to a "musical number" where they uselessly tamp to "Drill ye tarriers, drill", not real work. We never see rails being bolted together.
The story line depends on the fiction of surveying being just ahead of construction.
Regarding your last point - if they'd stuck more closely to the history, where would the human drama be? Ya need that kind of thing to make an exciting film about an engineering challenge. Labor troubles and infrequent Indian attacks and arguments over the route would not have been very entertaining unless personalized.
--If they move, kill 'em!
A Hollywood movie - historically inaccurate? No, really??
-- It don't mean a thing if it ain't got that sting
Not so much because it's Hollywood.
In fact, the majority of all Westerns (novels, film, games) are historically, very inaccurate, even the New Westerns.
The 'Wild' West everybody knows is simply a created mythology.
It's rather pointless to complain about a Western being unrealistic.