While many of your points are valid, I don’t see the author as a misguided person who has made a temporary, superficial discovery about interpersonal relationships. Having gone through a lot of this myself, I see the author as taking a huge first step towards the growth of his emotional intelligence. He implies that he has a history of speaking his mind (with a lack of tact). Now he is learning to emphathize and have pleasant relationships. The next step is learning to balance those things. Speak your mind when doing so is important, and consider the impact of your words while doing so. Sometimes telling someone a hard truth is the true kindness. As the author points out, the way you deliver those messages determines whether they are helpful or just hurtful.
I don't mean to send a harsh personal judgment about the author, by the way, only his message. The zeal of the convert is something that happens naturally to everyone when they discover something that opens up new possibilities for them, whether it's a social technique or a programming language.
I suspect that the author meant this in non-intimate situations, however I agree with your general trend of reasoning. These types of people are comforting to the extreme, I would assume that would (technically) make them satisfying friends and lovers. I'd love to see a clarification of your use of unsatisfying here.
On a not entirely unrelated note, people will also use empathy to respond to requests for things. You can spend years with someone before you learn that expressing empathy is their way of avoiding saying "no." (You'll figure this out much faster if it's a working relationship instead of a romantic one.)
Empathy can be a powerful, powerful force, and it can act on either party.
I'm not comfortable with this as a general strategy stemming from a universal mantra. Learning this as an adult is impressive and probably exceptional, but it's a phenomenon we're all familiar with. We all know people who behave like this reflexively and have done so their entire adult lives. It can be pleasant to hang out with people like that in a heterogeneous group where not everyone is comfortable with everyone else, but they make damned unsatisfying friends and lovers. Policing comfort zones is a sure-fire intimacy killer, and it isn't exactly a triumph of empathy to avoid uncomfortable topics of conversation, even if it requires prodigious skill at empathy. Children of troubled and violent households, such as Bill Clinton, are the poster children for glib empathy that is a mile wide and an inch deep. (No political aspersions meant, by the way; I liked him as a politician and a president.)
I would argue that in this case we are seeing a misguided (and probably temporary) "zeal of the convert", and by convert I mean someone who has discovered the practical value of this Clintonesque "emotional easing." Emotional easing is much like quantitative easing: it shifts unpleasantness out of the current context. It's a valuable tool, but it can't be applied universally. I'm not comfortable calling it empathy, either. "Perking up" when another person's uncomfortable emotions come to the fore and steering the conversation away teaches them that their problems are their own, and that their full selves are excluded while a partial self (with unpleasantness filtered out) is welcome. That's appropriate in some social contexts, but not all, not by a long shot, just like quantitative easing is only appropriate in certain contexts. And it's the opposite of empathy, even though executing it requires a limited use of empathy. Empathy means feeling what another person is feeling because your human bonds transcend the difference between you, not strategically tapping into their problematic feelings so you can override them with your own more attractive and pleasant ones.