ObsService.getComplexObs(..), is marked as deprecated. Documentation of the method suggests to use ObsService.getObs() instead.
However, currently ObsServiceImpl.getObs() does not fetch the complexData like getComplexObs() does, by invoking the associated handler.getObs(obs,view) if the concept datatype is complex. Same should happen with getObsByUuid(), which should also invoke the associated handler if the concept datatype is complex.
More in talk topic: https://talk.openmrs.org/t/obsservice-getcomplexobs-deprecated/12188/9