I can't speak as to how the current open house hours in the Club/Lab compare with the open house hours on our September 2012-2014 sailings on the Disney Fantasy. But, I will say that even though there seemed to be a lot of open house hours back then our experience was generally positive. I'm guessing this has a lot to do with the age of the children you are travelling with. In our case, our son was only 3 on his first sailing and 5 on his third sailing. Given the large age disparity in the Disney kids club relative to other cruise lines, our son was understandably shy around the older kids when he was 3. (The activities can get so frenetic in there at times that it looks like controlled chaos. Lol.) Consequently, despite the fact that he was desperate to play in the club, he didn't want to be there by himself. (If only he had an older sibling or a friend with him, it probably would have been different.) So, the only time he spent in the Club were during open house. When our son was 4, it was much the same as the last cruise. Then, halfway through the cruise he suddenly decided that he was ready to go it alone and absolutely loved it. When he was 5, he wanted to spend every waking moment in the Club and was bummed when he had to go to the Lab for secured programming during open house hours in the Club.
Our experience may only apply to a select group of cruisers traveling with an only child, shy/young child, etc. That being said, the open house hours (in the Club, at least) did seem to be set at times that could best accommodate these families with the least amount of inconvenience to everyone else. The Club had open house hours in the early morning, with the obligatory character appearances and activities that were generally targeted towards younger children anyway. And, the Club had another open house for a couple of hours in the late afternoon/early evening before main seating for dinner. A great opportunity for my son to run off some steam before being asked to sit an extended period of time for dinner and a show. After dinner, I think it was all secured programming in the Club/Lab.