Even in Middle Earth. This can't be classed as a problem with the movies, the issue exists in the source material as well.
Throughout both The LoTR and The Hobbit, the heroes are mostly invincible. Aragorn and the Nazgul on Weathertop, the Mines of Moria, the Orcs at Amon Hen, Gimli and Legolas at Helm's Deep, and so on and so on.
Even Boromir was nigh-on unkillable at Amon Hen and only died because Tolkien needed him to. The book has him "pierced by many arrows" and the heroes there had a kill-ratio of at least 10-1. More if you discount the hobbits.
If anything, the kill-ratios were lowered for the movies. Read the LOTR Wikia entry for Amon Hen http://lotr.wikia.com/wiki/Skirmish_at_Amon_Hen for a comparison.