I thought it constituted a full engine, curious on your take.
Two reasons:
- It is often a last consideration for web devs. If I had a dollar for every time WebKit broke just at my work...
- I don't like Apple, so since it's my dumb comparison, they get demerits for being a stupid walled garden that's hard to leave.
It's mostly that last one for me. It's indeed a valid engine, but my understanding is that it's not particularly great to work with. Either way, you can just take my comment as a thinly veiled dig at Apple.