Agreed: accurate assessment of a contact's altitude is important....
But, in a purely military sense, when using such a ground-based radar in an air defence scenario to direct fighters (Malaysia for eg has Mig 29s, SU30s & Hornets) toward such a target, approximate is good enough because the fighter radar will be far more accurate. It's not about arranging or monitoring deconfliction, it's about getting the fighter radar pointed into the right piece of sky in order to be able gain radar contact in its own right which then allows a target to be intercepted.
In the absence of imminent hostilities I imagine that Malaysia's Air Force, like many others around the world with similar risk assessments, is faced with the same compromises wrt the costs of systems calibration and around-the-clock monitoring: hence the somewhat discredited altitude data from that source.
Just a humble opinion.
