The "problem" ,i.e. unfairness , of the DRS is that although the Complainant can use a Trademark to invoke a DRS a Respondent cannot use Trademark LAW to defeat said DRS, otherwise the Complainants would not win 90% of time, as they know full well.
Since the Intel case in the ECJ the task of proving passing off etc is much harder ,and thus the easy route for companies is DRS.
WS