The cutscenes indeed looked a lot better than ingame stuff. I really hope it's ps4, but the leap doesn't seem too huge. It's probably to be expected because there's so much you can push realism at some point it just comes to how much detail you can render in real time, resolution and fps.
Nah, it's just the team neither has the time nor the money to invest in this title I feel. You can only do so much in a series that makes 90% of it's sales in Japan which is why it still does not seem like a massive leap from Yakuza 5.
It is a shame but it is what it is, it's why Japanese developers have struggled so much the previous gen. Hopefully art direction, which they always seem to excel at, can make up for it. Sonic Unleashed, Generations and Lost World all do this and it works out just fine.