I've noticed that it's movements are kinda correlated with bitcoin's movements.

Are you talking in terms of USD value or BTC value? Its price in BTC is meant to inversely correlate with BTC's USD value.

If it keeps this correlation, a very large and fast drop in bitcoin's value could mean a fast drop in sdb value

The SBD is a token that can be converted (with a 3.5 day delay) to roughly $1 worth of STEEM. It is this guarantee floor that keeps SBD pegged from below. The theory of pegging from above comes from emission of SBD. If over time it's observed that the pegging pressure from above is inadequate, then we can address that with a limited STEEM->SBD conversion option.

But for now, because of the botched reward pool migration in HF17/18 happening concurrently with irregular market conditions, the recent experience with SBD price isn't enough to say "let's kill SBD." We're on track to it normalizing.