Hi... I would respectfully like to challenge your analysis. Charter Trustees have no administrative role (other than selecting a figurehead mayor), and spend almost all of their budget on their own staff and meetings. BCPs own website even says they are non-statutory. The Trustees themselves are not elected to that role - they only become Charter Trustees ex-officio as they are elected BCP councillors for those areas. The mayors are similarly not elected to that office, but are selected by the Trustees from among themselves.
I am therefore not convinced that they qualify as an independent "layer of government."