If availability on every partner was supposed to be equal for all partners, then they may as well abolish all frequent flyer programmes and bring in a single Star Alliance FFP to replace the individual airlines'competing programmes.
Yes, the ST airlines are "partners", but they also compete. Most airlines run their FFP to make profit so no airline is, in an extreme example, going to stand by and watch their award seats predominantly end up booked in a rival programme where that redemption may be something of a bargain compared to their own.
I am surprised at how frequently it comes up all across FT that people expect to see the same availability across all their programmes of interest; the programmes are all different, with different qualification targets and different mileage earning rates.
So the expectation that redemptions should be equal across the board, when there is such a variation in earning and burning rates is, I think, somewhat naive.