Advice: Installing toilet in existing bathroom

Hey guys, just looking for some advice regarding our main bathroom. We have a 1980 built house which has a toilet separate to the bathroom and was hoping to move the toilet into it and make the house more modern.

A plumber came round for a quote but ended up telling us that if we cut into the floor and cut the waterproofing we would have to redo the whole thing, meaning we might as well do a whole new bathroom at the same time.

Were in Queensland, has anybody else had to do this? Is this plumber pulling our leg?