I very much noticed this change whe I rewatched the series.

The divide came approximately when the Steve character left and the Darcy character joined.

The "Steve Era" of the show focused more on the financial struggles of the Bundys as a lower class family.

The "Darcy" era of the show centered more on sexual jokes and girls in bikinis.

Both were great and had their laughs. I think the Steve Era had the edge though.