I say it's both. If you don't know how to speak, how will attitude be important? Vice versa.

Hmm.. tell me something, did u happened to have gotten abused by some english speaking ppl when u were a kid or something?

As for your examples:
Person A: just 'cause he's likeable, does that mean he's going anywhere?
Person B: linguistic skills alone is useless unless one plans for that to be their career path.

Obviously pathethic examples there.

Fact: attitude towards language also counts as attitude. Hence the two are very interelated indeed. Nobody is talking about being able to write something like the works of shakespear here, but being able to at least write properly is rather important indeed. Ever had to proof read a technical document written in bad english? Its not funny, I can tell you that, not because I'm fussy over the language or anything, but because the possible meanings in it r so damn blurred out that there can be the risk of a law suit should I ever approved of that document being passed over to the client.

ie good in english and at the same time, displays good character and attitude.