I don’t doubt that northern hemisphere "western" countries will have similar peak periods due to having similar religious and school holidays, as your quoted dates suggest. And currently Ramadan has some overlap with Easter too.

But the peak seasonality of demand ex-southern hemisphere may be different. As might departures ex-China for example around Golden Week or Chinese New Year, both of which are widely reported as being some of the largest mass movements of people on the planet. And both of those fall during off peak seasons in, say, Europe.

As you rightly say, airlines will base peak season pricing on expected demand for travel. But if QR has adopted a single global seasonality system based only on western European or north American peak times then they may have missed a trick, which seems unlikely. That is why route or sector specific data points could be very helpful