it all has to do with the type of parts used as well as the quality of the parts.
you can have the highest quality barrel available but if it's a 1 in 9 twist it's not going to be able to stabilized heavier bullets(about 65GR). similarly a 1 in 7 twist barrel may be too fast and destabilize lighter bullets so a 1 in 8 is a great choice for all around shooting but still may not be the best with ultra heavy or ultra light bullets but with average bullet weights(55-67) it's a great choice.
a lot of high end ARs come with 2 stage match triggers but that is not a prerequisite for high price tag and anyone can drop a $100 trigger upgrade into a $600 DPMS and drop it down from 1.75 MOA accuracy to 1 MOA.
a lot of high end ARs come with free floated tube or rail handguards but that is also not a prerequisite. you can put a free float handguard on a $600 DPMS and drop accuracy from 1.75 MOA to 1.25 MOA.
those three features are what affect your accuracy the most and even a budget brand AR15 can be accurized and shoot just as well as a high budget brand. the differences are resale value, fit+finish, and overall appearance, if you would rather have cheap but functional than pretty and polished then get a Palmetto State or DPMS budget rifle and accurize it. if bragging rights is what you're after get a Larue Tactical or Seekins Precision and call it a day.
ignore my complete lack of capitalization. I still have no problem correcting your grammar.
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