Saudi Arabia has 2 such pre-existing stadiums. They didn’t meet the requirement (the South American bid did). But of course FIFA suddenly decided to relax that rule for Saudi.
Australia doesn't have meet those requirements either (most of the 40k+ stadiums are Ovals that don't meet the sightline requirements) so the rule relaxation benefits them too.
I'm not arguing who has the better bid. The point is that loosening the requirements benefitted Australia too, not just SA.