Doesn't it really just come down to which party holds the SCOTUS majority?

No. You don't have any constitutional rights to consume marijuana, alcohol, or tobacco. Your state government is perfectly free to completely ban any and all of those substances, and you would have no constitutional claim to present to the Court that they had done anything wrong. The states don't altogether prohibit tobacco use or alcohol (though many still prohibit most private recreational marijuana use) - but all of them could.

Firearms are thus different, under current SCOTUS precedent. The Court has held that you have a constitutional right to bear firearms, and a state law that banned firearms altogether would (unlike alcohol or tobacco) absolutely be unconstitutional under that precedent. When confronted with a tax on newspapers - another constitutionally protected activity - the Court struck down the tax as violating the First Amendment. I think the Court would similarly strike down a specifically targeted tax on firearms and ammo - especially if it was intended, in whole or in part, to discourage gun ownership or use.