@DerFurst ...my friend, see here, the issue I see is that you're trying to justify an in game rule by using background material.
It doesn't work like that. When it comes to the actual rules and how the game is played, the background material is completely irrelevant. The only thing that matters then is the rules as written, and per these rules, the Interdictor is NOT a star destroyer. What the background or canon material designates it as matters not a single bit. Only ships with the specific wording 'Star Destroyer' in their card names can use it, and that's ISD, VSD and Gladiators.
Now of course in a fun casual game, you can do anything you want! But in a tourney setting, this is not allowed,more the rules.
I always try to keep the background material separate from gaming rules...it's less confusing that way!