This is very true. I know of one case whereby a HI of a land div was ordered to change his assessment of an OMS. This HI, as with those who worked with this OMS knew this chap wasn't an officer and a gentleman. Years late, this OMS had to resign as a result of his case which was reported in the ST.
Similar things happened in the SAF during my time (old days), where the following probably explained why very few SAFOS are ranked less than o/s or excellent:
1. say a CPT or a MAJ who is a non-scholar indicated that the SAFOS LTA is above average, not excellent, the senior officer has to provide a detailed explanation as to the reasons that the SAFOS officer is not excellent; and
2. eventually, numerous non-scholar officers do not write performance appraisals for scholars which are other than excellent or outstanding, also because in a few short years, the scholar officers or SAFOS officers will be promoted faster and higher than his previous superior.