You buy a class, not a specific seat. The small print always says due to operational conditions the aircraft may be changed at any time, and the configuration may change. Yes, you can book a ticket on a Qatar flight that is scheduled to be equiped with a Qsuite, but there is no guarantee you will get it.
There's actually a phrase been coined now "being Qatared", meaning you booked a "Qsuite" flight, and got shafted when a plane with a standard configuration was re-routed instead.
And, just to stick my 2p worth in too.... Beauty queen? Er, no!