I do not ask, "Why is Bathsheba the worst?" I do not ask this because you and I both know the answer: Thomas Hardy hated women. We know this; we have come to terms with it; we move on.
However. Gabriel still needs to be explained.
It would be bad enough if all that stood against Bathsheba was how she treated Gabriel. She is consistently and indifferently scornful and insulting. But you know men who put up with this from women. They're morons, but they exist.
But there is also the piddling consideration of people's lives. Bathsheba is responsible (with a fair degree of directness) for the deaths of two men. One, her husband. The other, a man she drove mad with uncertain hopes, who killed her husband for love of her.
These are not her fault, I hear you cry.
She should not have married Sergeant Troy (thereby killing Fanny Robin, incidentally). And I have no sympathy for her, because he was clearly a jackass all along. Honestly, if you fall for the line, "If you don't marry me today I won't want to marry you tomorrow," you get what's coming to you.
Furthermore, she should not have ruined Farmer Boldwood's life. That valentine is unforgivable in itself, but less forgivable still is her behavior thereafter, which seems to be calculated precisely to raise the poor man to a perfect frenzy of frustrated hopes. It is amazing that he stopped shooting after Troy was dead.
Bathsheba Everdene's butcher's bill stands at two men and a woman (and her baby). Gabriel Oak, you are intelligent and capable, and you appear to have some sort of moral sense. She has treated you and everyone else badly. Positive reinforcement is not in order.
What the hell is your problem?