There are instructions online for removing systemd; I think it is cause for regret that there isn't an install option and a commandline tool to "just do it". It's not tricky; it's just a nuisance that you have to do it at all.

[Edit] And a debconfig thing. It should be that easy to switch.

[Edit 2] I deserve to be voted down, I realise! I called for a change that I claimed was easy, without offering a patch! I should shut up, and my remarks should be very pale grey.