Nowhere in Bonvoy materials is it published that upgrades are prioritized according to elite levels. It has never been like that with SPG and it does not appear to be the case with Bonvoy as well. If the number of upgradeable elites arriving on a given day exceeds that of available suites,the property has a tremendous leeway in deciding who gets upgraded, and it will most certainly prioritize according to loyalty to the property itself (not the program), duration of stay and rate rather that elite tier or number of nights stayed with Bonvoy.