Nobody's mentioned the biggest Pyramid flaw to be fixed: The WC was originally supposed to have ten categories, not six; Bob Stewart concluded that nobody would be able to get 10 categories in 60 seconds and so covered up the bottom row.
As for the 6-in-20 versus 7-in-30, I think something easier like 7-in-30 is better. I'm not a producer, but I think if you have celebrities playing, you don't want to insult them by making them look like terrible players. At the same time, you don't want to make it too easy to win the big money. 7-in-30 made it easier for celebrities to look good (as well as helping out new civilian players by letting them ease into the game). Not only that, but too many times on the Osmond Pyramid we saw teams getting only 2 or 3 answers because there was a difficult word in the middle on which the team spent too much time. Not only that, but there were far too many games that ended after only five categories were played.
But Osmond's 6-in-20 has a bigger flaw, I think: the producers effectively switched the difficulty level between the two parts of the game. Their front game was hard, but it seemed far too easy to win the money in the WC, which seems a very bad thing to me.
(Some here denigrate the front game of the Clark Pyramid by saying it's too easy, but I think the front game is underrated, and is almost as good as the WC minus the tension. The Clark-era front game wasn't easy; it was deceptively simple. Of course, Bob Stewart was helped by having a small group of celebs who seemed to enjoy playing Pyramid precisely because it's challenging, not in spite of the challenge.)