There is nothing in EC261 that I am aware of that covers rebooking etc when an aeroplane is diverted - or if there is and I have missed it, please do point to the article

Qantas seems to have done exactly what would be expected - sort out accommodation whilst the issue is resolved.

The only difference that I can see for a BA flight would be possibility of compensation for the delay as long as not classed as an extrordinary circumstance that could not have been avoided

Qantas is a mediocre airline ime, but what it did is no worse than what other airlines would have provided