Something which should go without saying in threads like this is the definition of “diminishing returns.”
In this context, it’s fairly obvious that “diminishing returns” means “continuing to spend more without gaining as much performance or quality.”
“Diminishing returns,” isn’t necessarily the same thing as “negative returns,” more appropriately known as “losses.”
So simply, yea, in general, and almost unilaterally, spending more on an AR does buy a better AR, but less and less than the dollar before. $350-500 can buy a fully functional, reliable, and reasonably accurate AR-15. $500 more does buy a better AR. $500 more DOES buy a better AR still, but the gap between $500 and $1000 and $1000 to $1500 is smaller in performance and quality. $500 more buys a better AR still, and $500 more than that, still can a better AR than that, but by the time you’re spending $2000 or $2500, or more, on an AR, you’re obviously in a niche where specific application parameters levy very, very specific demands, dictating a very particular AR.
But… “objectively better” for the application remains to be “objectively better,” even if a dollar is buying as much difference as was bought with a dime at lower price points.