So the moral of this story is smaller doesn't neccesarily mean better or more profitable.
But the story isn't complete . . . yet! We haven't fast-forwarded 5 or 10 years ahead to see whether Austrian is a stronger airline as a result of this fleet replacement. They just
think they can make a difference, this is their business case, so now they put it to the test. Hopefully they are right, but time will tell. Interestingly, the article mentions that the goal is to "bolster its competitiveness with higher volume and more attractive fares." No mention about profitability (you simply deduced this), but Qatar Airways has big jets (in fact, they even ordered A380's), very competitive, great volumes, attractive fares but how many millions of $$$ it loses daily is highly confidential.
What the "others" are doing got me trying cigarettes in high school. Logic? All the "cool" kids smoke. The nerds do not- they are busy in their books. Other even "cooler" kids were trying harder stuff (something I, fortunately, was never brave enough to do) and talking about the wonder of it all. I contented myself with trying to learn to fly a Cessna 150 rather than "flying" by myself. The benefit of looking back at it after a few decades experience revealed that none of what the pack was doing was such a good idea afterall.
The airline business seems to be a little less clear about it's own issues. Getting big airplanes might be a great idea. Or it could be the error leading to death.