The buck stops with the executive committee and the Owner’s Corporation. Managing agents sometime run things by default because the committee or OC doesn’t. However, the committee and OC have the authority to instruct the managing agent, even against the managing agent’s advice or preference (so long as it would not be illegal). The managing agent should give advice to the committee and owners because they are employed by the OC to be expert in OC management but ultimately it is the committee (or the OC at a general meeting) that is responsible for decisions.
The managing agent’s function is simply to assist the committee undertaking its roles. So, for example, a managing agent might do all the mechanics of accounting, receiving levies and paying invoices for services and products to the OC, but the treasurer is responsible to satisfy the committee that those functions are being performed properly.
If the managing agent is saying or doing something you don’t like, talk to a committee member. The committee represents you as a member of the OC. The managing agent is just an employee of the OC, albeit one who might be able to provide good advice to any OC member or the committee.