It’s just that they use the common, high fructose corn-syrup version of Coke. It leaves a sour aftertaste and is horrible for your health.
Those of use who grew up on original Coke made with real cane sugar hunt for it where it can be found. Real sugar Coke is kosher; you can often buy it in our large grocery chains around Passover time. Also,some Hispanic bodegas sell it because it is bottled in Mexico.
No HFCsyrup Coke can beat that flavor of real cane sugar.
For all the reasons you cite, I’m convinced New Coke was a head-fake to cleanse the palette from the memory and the stocks from the warehouses of The Real Thing.
If the switch in formula had been straight from sugar to HFCS, customers would never have borne it. New Coke was no improvement nor substitute (despite the hype and campaign that surrounded it) and “return” to “Classic” tasted _close enough_ to The Real Thing that no one objected to the sugar to HFCS bait-and-switch.