Magnet and charter schools have a lot in common. You could look at state charter school statutes as encouraging school districts to be proactive about setting up academy model and magnet schools.
No, that doesn’t reflect the situation. Charters enshrine the public school revenue by allocating some of it to “better” schools. They make it harder to lower school district revenue as they (in the eyes of parents) make the established system work better.
That’s different than aiming to reduce district tax levied. I’ve read a variety of statements from charters themselves, including that one. There are also proposals to privatize administration of school districts using the same reasoning. In education, no matter who is speaking, typically the focus is on performance, retaining teachers and meeting more diverse student needs.