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Do you "need" additives?
Couple of assumptions: 1) oil doesn't have much affect above the top ring, 2) "pure" gasoline is a better solvent than lubricant, and 3) gasoline contains unstable components that lead to deposit formation in high temperature areas in the induction system such as injector nozzles or valve stems - mostly from the 'heavier" components since the lighter ones evaporate away when the engine is stopped.
So why additives?
Lead used to be the prime lubricant in fuel. But those days are long gone. Not sure how long various "detergents" have been used. So what lubricates the valves, AND keeps the deposits from clogging injectors and sticky rings? Only thing left is the additive package.
I'm not a chemical/automotive engineer - don't know what's in those additives - but it's gotta be tough to balance detergents with lubrication - normally mortal enemies.
So, IMHO, buying the cheapest stuff with a bad detergent package only risks need for the occasional fuel system cleaner. Buying the cheapest without a good lube additive risks valve recession in the head - who remembers aluminum heads without hardened or steel valve seats when lead was phased out?
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