Both Van Gaal and Ole did better than him in the league, which is the main barometer of success. And both did better than him in UCL, despite being quite shit there.
Moyes season was somewhere between EtH's first and second season, and miles better than this one. If we are counting interims, Rangnick's terrible season was still better than our last season, and far better than this one. So yep, at best case I'll rank him just above Moyes, but below Ole/LvG and considerably below Mourinho. But considering the money spent, and time given, I would rank him bottom, and think that together with LvG, long term he has been the most damaging manager we've had.