Team builder has a significantly more difficult matchmaking problem than draft. It's trying to adjust for player skill with a given champ, allow teams to be built by a captain rather than just a numeric comparison, and match specific role/lane selections into teams. Add into that the crushing lack of competent players queueing for support, and until recently the relatively low pop of the queue, and you're just asking for impossible matchmaking problems.
That said, the bad stuff is significantly bad when it happens. Yesterday I played a game where a gold 4 Vayne got matched into a game featuring 3 masters, 5 diamonds, and 1 plat. Needless to say, Vayne got mercilessly stomped to something like 1-12-4, her team raged at her for losing the game (which was accurate), and it was a generally awful experience for all involved.
I would really like team builder to work, as it's a great way to practice a particular champion, but it seems we have the same problem we've always had -- too few supports leading to long queues for other roles, which leads to few teams being made, which leads to matchmaking of dubious quality.