I think it would have made it slower than it is under Trump.
Based on what, though? There were zero restrictions on Israel under Biden and Harris. They didn't even acknowledge that a genocide was happening, much less do anything to stop it. When asked what she would do differently from Biden, all Harris could come up with was that she'd put a Republican in her cabinet (don't laugh!).
I think it's got better odds than letting republicans in, especially when they're so determined to gerrymander and otherwise secure their power undemocratically.
This is just another way of stating, contrary to the evidence, that Harris would have somewhat mitigated the worst of the genocide. If your goal is to stop the genocide, Biden whole-heartedly supporting Israel while observing the formalities of democracy is no different than Trump whole-heartedly supporting Israel while gerrymandering. Republicans keeping Democrats out of power doesn't make a difference if Democrats are going to rain mass slaughter down on the world, too.
Democrats by and large have failed to uphold the formalities of democracy, anyway. The bare minimum for doing that at this point would be things like jailing a bunch of the Trump administration and packing the Supreme Court, neither of which are on the Democratic agenda.