It's been decided, she's a Superdreadnought. There is no getting around it.
When comparing her to the Archangel-class, I realized that the Archangel's status as a dread is centered around her weighing in at 310 million tons. Legendary's size and weight is easily 510+ million tons (haven't done the math). A jump size by that much (getting close to double) is clearly the status of a Superdread.
This one is going to take a while folks. So bear with me. But there is the latest wip with the Archangel-Class Gun-dreadnought.