Is Arco gasoline inferior to other gasoline brands? If so, then why?

Gasoline prices are are very painful to pay nowadays. And Arco gas is usually the least expensive gas around. But for years various people have told me that Arco gas is bad for my car but I’ve yet to hear a good reason for this. “My mechanic said so”, isn’t good enough for me. Is there any valid reason those claims and if so then why? Is it really significantly better for a car’s engine to function using more the expensive gas sold by the likes of Shell, 76, Chevron, Mobil, etc.?

Perhaps this is just a rumor that is being spread by one or more of the more expensive gas companies to scare people into buying their more expensive gas?

FYI: I have used Arco gas far more than half the time on my previous vehicle and got over 300K miles out of it before selling it. Also it always passed State emissions tests.