I don't know how it works for auto parts, but my experience in supply chain quality management tells me there is room for differences across brands that are selling the same part from the same manufacturer.
Not saying this happens for cams at all, but imagine the true defect rate at the manufacturer is 5%. Then imagine Lunati's contract will allow only 1% returns before they financially penalize the manufacturer, but Summit doesn't put any limits at all on return rates. The manufacturer might decide to 100% test shipments to Lunati and charge them a little more, but might test only 1% of what they ship to Summit.
The good part of this is the manufacturer is likely to improve the overall quality to avoid that testing cost for Lunati and all of their customers benefit...
This is hypothetical for cams, but it's a very real part of the world and is just one example of reasons for the "same" part to fail more when sold by one brand than by another.
There's rarely any data visible to us consumers and we rely on brand reputation and experience from those willing to share. Unfortunately, these anecdotes tend to skew toward bad experiences and often scare us if there is an "excursion" at the manufacturer or they choose to sell marginally defective parts or "seconds" to one brand that accepts the risk to gain a better price.
I personally believe a cam manufacturer won't be shipping total crap for very long and the odds
heavily favor a good experience, regardless of who is selling their parts.
I will also say the burden of "proof" on cause for failure of a part returned to a manufacturer is typically on the brand/seller. In the case of cams, it is easy for the manufacturer to blame failure of his part on the consumer or the lifters or the oil, etc., etc. which may in the end allow a higher rate of quality escapes for cams than might happen with other parts. How many cam and lifter failure threads on PY does it take to support this?
Which is all a way of saying the brands/sellers of these parts have a hard job and seem to do it well, given the complexities.
Life was simpler when a brand made their own stuff...