To reiterate the salient points: Commercial gasolines for a given market are essentially the same. Octane rating of the various grades is one major difference and is carefully controlled. During a production run, a CFR (Combustion, Fuels Research) engine - a variable compression ratio research engine that has been around for over 60 years - continuously samples the finished product for octane rating. This is part of the quality control function.
The other difference is the additive package, but each additive package is blended to pass the same standard tests, so any attempt to say one is better than another is subjective, at best.
Guys continue to assert that Brand A is better than B because "my car runs better with A", but it's all in your head!
The final differentiation is price, which is what I use to choose brands. Whoever has the lowest local price gets my business. My cars range in age from 12 to 40 years, and I have never had any fuel system problems with any of them.
The final point is that "modern" high compression engines with a knock sensor(s) and electronic engine control can be successfully operated on regular grade fuel, even if the manufacturer recommends premium. Aggressive drivers might notice a slight drop in performance due to the less aggressive timing map, but the average driver is not likely to notice any difference in operating characteristics.