Dunno about that... Data is always capable of emoting
, in the sense of playing a role. He fakes it with the best of them in, say, "In Theory". He might draw a really sharp line between emoting and having genuine emotions for this very reason: he knows he can fool anybody, but he has his own obscure criteria for what "genuine" emotions should feel like, and he can't be convinced he's meeting those criteria.
OTOH, there are moments where Data is deeply upset, particularly whenever his pal Geordi is in jeopardy. But in those cases, it would be natural for any character to act emotionless - the more so, the more deeply the character feels (c.f. Spock and other Vulcans).
I thus can't quite agree that Data ever gets depicted as being incapable of doing what he does here - emoting as per stereotype - because he actually does that quite a lot. And I don't think this is a particularly good basis for arguing that Data's emotion issues are unconvincingly portrayed.