Even if they'd gone with the original ending...

...it still wouldn't have worked.

Like, even if we overlook how bad it all looked (slow motion shark standing on it's tail and roaring, tomato juice-esque blood spurting from its mouth etc.), the whole concept of a unstoppable killer shark getting speared by a prow and dying from said injuries is just so half-assed and anticlimactic.

Could they not have made it so that that makeshift electrical device of Jake's was explosive or lethal in some way???

Of course changing the ending the way they did was a terrible decision (among the many bad things this movie had going for it), but I can completely understand why test screening audiences didn't like the first one.