It doesn't have to be. Once TNG was down to its seven core members, they had no one below the rank of lieutenant. Ditto with DS9, which had a captain, three LCDR's (or equivalent), a lieutenant, and a noncom. VOY would have done fine with Harry as a LTJG. And if you need a bottom on the totem pole, just give Seven or Neelix a uniform. Neelix rocked the gold in "Before and After", and in "Relativity"... blue might have been a cool color, but Seven was just plain hot in it.
And in any case, the "naive ensign" idea was fine for Season 1, OK for Season 2, and pointless afterward. Competent showrunners would have found a new way to develop him. Alas for Harry, they were doing DS9.