In general I've found that Qantas availability is a bit worse than other FFPs around here, especially after covid, but I wouldn't say they're worthless. I've made a few Platinum seat requests in my time but most of my premium class bookings over the last 2 years have been seats available to anyone.
To be fair, I primarily travel between Australia and Asia, and for this I find QFF quite strong, especially with China Airlines as a redemption partner releasing quite a large number of business class seats (although this is gotten worse recently as people have been allowed to redeem flights onwards to europe etc. - I only use them for trips to Taiwan or self connect onto Japan/HK)
I collect points in 6 currencies: Avios (4 airlines!), QFF, Velocity, Alaskan, Krisflyer and Aeroplan, giving me access to redemptions across two alliances and a vast raft of non-alliance airlines; huge flexibility. Putting all your eggs/points in the Qantas basket is just loopy IMHO.
I think this depends on how you collect points. I assume you buy points on Aeroplan and Alaska, and transfer from Credit cards for the other 4. In practice I find that the yield I get from Credit Cards (both for spend and sign-up bonuses) is lower for other programs compared to QFF or Velocity.
I'm not sure how many points you earn a year, but I think for many people collecting points in 6 currencies isn't actually a viable strategy, since it means that they'll never have enough points in any one currency to redeem a premium cabin trip.
I definitely agree with you that for travel to Europe, Avios, Krisflyer, and to a lesser extent Velocity have better availability than QFF, and people should collect those currencies if Europe is the goal. In my opinion, for Asia, QFF is probably still better (taking into account the higher earn from cards).
I've recently started collecting Krisflyer too, but the recent devaluations from most card issuers for KF transfers really threw a spanner in the works.