I'm pro-Snitch.

Harry's gripe about the snitch, which is that it trivializes the rest of the game, isn't the problem on display here.

The issue currently afflicting the user experience is that the House Cup doesn't just rely on Quidditch Win/Loss, but also on the magnitude of the win/loss. Therefore, two teams can collaborate to play a game of such magnitude that it obliterates all other considerations.

A clock wouldn't actually solve this, (they could just agree to exchange points for the first X minutes, then play for real for an abbreviated endgame when time pressure became acute).

A solution to the problem must prevent Quidditch collusion from making one of the last two teams to play Quidditch automatically win the House Cup, but simultaneously maintain the primacy of Quidditch in determining the House Cup (because otherwise students won't care about the House Cup).

A simple solution seems to be that rather than adding the points of both winners and losers to their Houses respective scores the winner is awarded a static (high) number of points.