If you get 8th with Bigglesworth, you get absolutely no value out of the Hero power. Kind of like Alexstrasza, except you don't have much control over when the benefit comes. And when you do get the benefit, you're getting a minion from someone that died, which sounded great at first, but now that I think about it - if they had good minions, they probably wouldn't be dead.
I am guessing it's going to be pretty crappy until you get people dropping in 6th-4th. I can see the hero power giving you just enough to make it from 5th to 4th or 4th to 3rd, which is significant.
I played a game last night where the compositions in the lobby were: Me (beasts), Pirates, Murlocs, Murlocs, Murlocs, Murlocs, Murlocs, and Murlocs. Pirates went out 8th and I ended up taking 3rd. First and second came down to big divine shield poisonous murlocs vs. bigger divine shield poisonous murlocs. I managed to survive until 3rd, and the divine shield poisonous guys wiped out everyone else. Quite compelling.