Tosafos wasn’t talking about Mitoch, only about Tzorach Achila Mamesh. Even if the electric burner would be Muttar to turn on that would only apply to the burner but not to turning on lights.
I just wonder about an induction stovetop, where you aren’t competing any circuit. In that case, if it is set to a setting that it cannot boil, would you be allowed to warm up water on Shabbos Lechatchilah? I guess that’s where Zilzul comes in.