The BUCS rules are presumably to encourage games where otherwise teams would be inclined to postpone/concede. Usually teams would just concede with 10-12 players so clearly the rule is an attempt at stopping that, not so much punishment as much as encouraging games to take place. If you think that's a punishment, wait till teams don't travel because they don't want to be on the end of a 17 v 10 match (with the inevitably injuries too).
If a team is turning up with 10 players, they're going to be the only 10 players they have available, regardless of ability. You should be able to find the weak(est) players quite easily.