I’ve never tried Sergeant Russet, but there is another GD russet, Razor Russet, which I tried and found to be not that great. It has these really big lenticels which can be sources for fruit degradation, and it tastes more bland than Hooples. At least for me it did. Sergeant Russet could be the same as Hooples but in the USDA database it has its own unique entry which makes me think someone thinks it’s different. It does look a lot like Hooples. See a past thread here, Sergeant Russet apple, anyone heard of it?, for more info on Sergeant Russet.
Re: the original GD vs Hooples, I never grew an old strain GD but have tasted it over the years and my memory is it is not too different from Hooples. My guess is in a side-by-side the Hooples will be a bit more intense. In general russeting adds a bit of intensity. For example I have King Russet which is a russet sport of Reine des Reinettes. The trees are side-by-side and the KR is a bit more intense than RdR. Unfortunately both are fireblight magnets, I love them but am not sure they will be staying.