yes, accuracy and reliability are similar to an extent. When you take into account differning barrel profiles, free float handguards, trigger upgrades, different gas lengths, chrome lined v. non-chrome lined barrels and chamber, MPI, Nickel Boron coatings and all the other stuff that enhances reliability & accuracy, you can have quite a stark contrast in reliability & accuracy. It just depends on what you are willing to pay. The AR is so modular and so many parts exist that there are probably billions of different variations you can have, again, it is up to what you want to pay.
What are the rifles configured like that your dad is looking at? 16" barrel, collapsable stock, rails, heavy barrel, etc.? That will give a better idea of the reason for $200 difference in price. But, just based on my experience with Stag (none with Armalite) and the fact that Stag has a better warranty, I would go with them.