Why would Assembly Democrats prefer a Republican state senate? I'd assume Democrats would want to control both chambers.
Assembly Democrats get to gerrymander their own chamber in exchange. So the majority parties of both chambers vote for this. So it easily passes, but would fail a veto override.
If passing legislation requires an identical version of a bill to pass through both chambers, what good would it do to vote to gerrymander half the state legislature out of your control?
Wouldn't NY democrats be better off with 55% of both chambers rather than 65% of the Assembly and 45-49% of the senate?