I have said that what matters is the total amount of ingested fructose, not its source. Eating large quantities of dried fruits can have the same effect as eating too much sugar or HFCS.
Besides HFCS-42 and HFCS-55, there is also HFCS-70, with an even higher amount of fructose.
I agree that saying that HFCS is bad without giving more details about what kind of HFCS is meant is ambiguous.
That does not change that at equal amounts HFCS-70 or HFCS-55 are more likely to provide excessive fructose than sugar, even if HFCS-42 is less likely to provide excessive fructose than sugar.
HFCS is also absorbed faster than sugar, which must first be split into glucose and fructose. This may be desirable during intense effort, but undesirable otherwise.
You said, "So excessive consumption of high fructose corn syrup is more harmful than excessive consumption of plain corn syrup or of sugar." This appears to be plainly false.
It is more prone to lead to fatty liver or obesity, because fructose is not consumed directly in the body, but the liver uses it to synthesize reserve fat.
So excessive consumption of high fructose corn syrup is more harmful than excessive consumption of plain corn syrup or of sugar.
Nevertheless, the source of fructose does not matter much, but only the total amount that is consumed.
It is recommended to avoid a daily intake above around 25 g of fructose per day for someone of average size and having a sedentary life style. This corresponds to 50 g of sugar, but with a lesser amount of high fructose corn syrup.
Very high amounts of carbohydrates including fructose can be consumed without any risk only when a proportionally high physical activity is performed, using the high energy intake provided thus (for example by athletes during competitions or intensive training).
The harmful effect of excessive fructose consumption has been used for several millennia, for making "foie gras", by force feeding geese with fruits.