The fact that a site in a public campground has a 50 amp plug DOES NOT imply that it was INTENDED only for a 50 amp RV! My impression by far is that the vast majority of public campgrounds that have a 50 amp plug, also have a 30 amp and a 20 amp plug. Though I realize you say that’s not the case at this park.
The fact that a tent is on the site also DOESN'T imply that a tent site went unused. Do the tent sites even have power? Sometimes, they don’t. Were you there when any of the tenters checked in? Did you hear them request that they specifically wanted those sites so that they can keep 50 amp rigs off of them? Or is it more likely that they wanted those sites because “it looks nice”, “it has a good view”, “it faces the water”, “it’s close to the bathrooms”, or “it’s next to the people I’m camping with”?
Even if the ONLY plug is 50 amps, In the absence of any rule stating so, it still doesn’t imply in a public park that it was intended to only be used by a 50 amp rig. That’s why adapters and dog bones are made. The price of the site is irrelevant, and none of your business anyway. If the tenter occupied the site within the rules and paid the fee, it’s his site!
Your argument for “common decency” would carry more weight if it wasn’t so blatantly obvious that it directly benefits the larger RV owners. Following the rules and using the established process for occupying a campsite IS common decency! If this bothers you so much, why don’t you take it up with the controlling authority (not the campground hosts)? Let them explain it to you, and if you don’t like the answer go talk to your elected representatives.
:):)