Having separate working groups make decisions on a single topic each doesn't work due to overlap. If the Committee of Environmental Protection and the Committee

Having separate working groups make decisions on a single topic each doesn't work due to overlap. If the Committee of Environmental Protection and the Committee of Energy Production disagree about the correct amount to subsidize installation of solar panels, you need some way to arbitrate between them. Even if there's no overlap in topics, they'll still compete for their share of the total budget. It's not like parliamentary systems don't have topical working groups already. If all members of a working group agree on a proposal and it fits within budget constraints, they can get it passed without much friction. Huge senates voting the party line on topics they're unequipped to understand are the conflict-resolution process for when there's disagreement on a topic. Being affiliated with a party is a compromise where you vote with the bloc on topics you don't particularly care about in exchange for having the bloc vote your way on topics you do care about, but they don't.