It seems to me that the charges of fluffiness come not necessarily from "softball" questions, but from the impression that the questions are strictly softball.

Seeing you interview, it's very obvious that you're a genuinely nice guy. You couldn't hide that without changing yourself for the worse. But you don't have to, because it's an asset.

Part of this interview focused on the question of how do you make interviewees comfortable? Comfortable enough to do the interview in the first place, and comfortable enough to answer the questions openly, without fearing that the interviewer is about to spring some trap on them.

I've also noticed you tend to apologize when asking someone a question you think is tough, but it's interesting to see the reaction, almost a "No, no, I'll answer it."

For questions that are particularly salient but awkward to ask, you should continue to use that same technique to push just a bit further, both to stretch your comfort zone, and to get a feel for the real boundaries of what people are willing or even glad to answer.