From the moment he first stepped on board Voyager, Harry was a Senior Staff Officer, a trusted Senior Bridge Officer, and the Head of Department for the Operations Division, AS AN ENSIGN.
Harry was the Voyager counterpart to Miles O'Brien, yet you don't see people whining about 'poor Miles'.
Harry didn't need a higher physical rank because he was already in a position of authority, and it was a mistake to make a joke out of his lowly physical rank because it cheapened his character and role on the ship.
Maybe you should write a letter to Wang about this.
In the pilot, Kim existed to be saved from Quark by Paris, to be Paris' friend and to be saved from the Caretaker. And worse, saved from a disease contracted during an alien's attempt at reproduction. Wang may have had a regular credit but Kim was never a major character.
But it's more likely that he was on the bridge primarily to be observed by Janeway and Tuvok. It seems to me that it was the crew losses that led to his de facto promotion to senior staff and department head. Which I guess is what led Janeway to be so complimentary to in Twisted, inasmuch as no, green ensigns generally should not be able to meet such responsibility so well. Dating badly is hardly relevant.
A mere ensign being a major department head and senior staff bespeaks great competence. In current militaries, such responsibility must be acknowledged with the appropriate rank. But this sort of thing gets into the question of whether Starfleet is a military organization, and people will never agree on that. But it is clear that not promoting Kim is not a black mark against the character, because if he was incompetent he shouldn't have been senior staff and department head.
On the up side, people can agree that they wouldn't like Kim any more if he was a lieutenant.