The spa/decking/sauna I would think would be the owners responsibility to move as that is not a body corporate maintenance responsibility.
This is a circular argument. The strata manager “thinks” it’s the lot owner’s responsibility, therefor it’s the lot owner’s responsibility.
I would be asking for less thinking and more facts. Ask for some documentation to prove that this doesn’t come under common property or “fixtures and fittings” which, in NSW at least, are part of owners corporation responsibility. May be different in Qld but it’s a starting point.
The strata manager is, for obvious reasons, keen to make life easy for his bosses – that strata committee – by passing costs on to individual owners. That doesn’t make it right.