I think a distinction needs to be made here between Reg Force BMQ and Reserve BMQ. Not in terms of level of difficulty (I am not in a position to comment), but in terms of the difference in commitment between the two.
Anyone can walk away from the Reserves at any time (unless on emergency call-up). The catalyst for this is often, as is said, conflicts with civvy-life. When you‘re trying to fit 2 lives into one schedule, decisions have to be made. In addition, given that it is so easy to quit, anyone who has not personally committed themselves will quit the first time they have second thoughts.
The Reg Force, on the other hand, is much more difficult to quit (although I won‘t pretend to know the process). So just because Johnny Bloggins had a bad day doesn‘t mean he can decide not to show up tomorrow. As well, the Army IS your life - you‘re not on a school soccer team, or taking violin lessons anymore - so priority conflicts simply do not exist.
For the reasons cited above, I expect that attrition rates on specific BMQ serials will be higher in the Reserves than in the Reg Force. Therefore, when discussing this topic it would be prudent to specify whether you‘re talking about Reg Force or Reserves.