Funding brings the police to the negotiating table faster and harder than some years-off change in law/precedent or union contract negotiation. That is as valuable as the actual defunding.
The right has defunded programs they couldn't abolish for years. It's a tried and proven strategy.
It's not the only thing to do, it's one of several things to do. Defunding reduces their access to weaponry and equipment and hinders recruiting. It's a big step toward abolition.
We live under Capitalism---let's use that to our advantage. Less money begets less power.
It's like energy in physics. You can worry about all the (perhaps more fundamental) mechanical, chemical, etc. interactions, or you can trust the conservation of energy and not fret over the details.
The right has defunded programs they couldn't abolish for years. It's a tried and proven strategy.