Now I'm not a Wizards designer.
Yet.
But just from looking at Thalia's card, she screams 'developer pet project' to me.
Now, clearly she is a particularly pushed variant of
Glowrider
, so I figure that some developer thought to himself "Is there any way we can make this better" and came to the conclusion that the legendary drawback justified the lower cost and first strike; and then they had to attach a character to it and looked for prominent persons from the style guide they hadn't used yet