Where you stand
What your management company is responsible for
In most modern leases the resident management company is a named party alongside the freeholder and the leaseholders. The repairing and management obligations sit with the company, which means they sit with its directors - and the directors are leaseholders who volunteered.
In practice that covers maintaining the structure and communal areas, setting and collecting a service charge that genuinely covers the cost of running the building, consulting leaseholders properly before larger works, keeping the block compliant with fire and electrical safety requirements, holding the right insurance, and keeping the company itself in good standing at Companies House.
Appointing an agent does not move those duties. They stay with the company. What an agent does is carry the work, give you the information to decide properly, and make sure nothing falls through a gap while everybody is busy with their own lives. Any agent who tells you they take the responsibility off you is telling you something that is not true.