What makes a shapeshifter a dragon?

[Dustin, Wyrm Master]

NDFL made me think of something. Since the dragons spend so much time as humans, are they really dragons? I mean, they can be whatever they want, so aren't they just called shape-shifters?

This isn't just a NDFL concept. Most dragons who can shape-shift, spend most their time as humans. They treat becoming dragons as a super power, only used when they need to knock over a building, then its back to being human.

What does it add and take away for you?

[Cassandra]

I haven't read this, but have read 3 other series where the dragons can shapeshift to human - Rogue (which wasn't very good), Firelight (rubbish), and Seraphina (which is great). In the first two mentioned, they spend most of their time in human form. Basically it feels like they're not really dragons, just humans with all the usual YA tropes who occasionally take on a reptilian form for fast travel.
The only one I've read where it felt like dragons to humans was Seraphina. They were obviously different to the humans also in the book.

To answer your question, I'd say that dragon/human shapeshifting only adds to the concept if they're truly not human, and have non-human behaviour. Or develop human characteristics, or play with human norms. Otherwise authors should stick with the usual dragon/human pairs of two minds that mesh together.