They give different predictions for the same observed event so both can't be true. For example, since there is no gravity in the standard model (the general QM-

They give different predictions for the same observed event so both can't be true. For example, since there is no gravity in the standard model (the general QM-model encompassing everything but gravity) and gravity obviously is observed, the theories are fundamentally incompatible. It would be a different situations if the theories actually covered different domains of experiments, but neither define such a restriction (and it wouldn't make much sense to either of them).