From a macro level, there is not a whole lot of difference from one vendor to another. Sure, your have a couple of bottom feeders selling out-of-spec parts and you have a couple of vendors that are way high on the dimishing returns scale. But since the AR specs are widely published and not hard to achieve, there are a whole lot of AR shooters that are shopping in the middle. There are a number of vendors of known quality in the middle range, so it comes down to who has what on sale when the consumer is ready to buy.
There are some websites devoted to the AR that seem to be run by a herd of label conscious teenage girls where only 2 or 3 brands are "the best". They offer the same old tired anecdotes to support the claim, but never any scientific evidence. I have shot with several dozen AR shooters over the last 30 years and trained several of those. The rifles involved have come from almost every major manufacturer I can think of, and more than a few minor ones. When there have been problems, it almost always was ammo or magazines, never gun parts.
My own philosophy is to assemble the best rifle I can for the price. Therefore most of mine are mixmasters. They are all accurate, durable, and reliable to a fault, and none of them cost over $900. Even before this current madness, I would see guys shelling out $2500 for just the rifle sans optics, and I just had to scratch my head and wonder. The expensive rifles do not shoot any better than mine, and they probably won't last any longer or be any more reliable.
One thing I do not scrimp on is bet-your-life magazines. My "go" kit contains nothing but Lancer AWMs. I will use just about anything for range mags, but the only mag I will trust my life to is the Lancer.