I don't think that using random form arrows necessarily means a better chance for weaker teams. If Giggs and Bellamy are on bad arrows, Wales are screwed no matter what. With them both on red arrows, they should at least be able to score against a 'better' team.
Plus the keepers of weaker teams have the bonus of red arrows to make them better (not that this makes any difference to the Wales keepers - believe me I know!
)
If not red then how about a different arrow?
If you use random arrows, you might have to make changes to half the team picked by the player which would make having the choice to pick players quite redundant.
Hmmmm.