It’s not that Mandau is /bad/ per say, it’s just that there are much better weapons that can be obtained for much less cost/effort, and generally when I see another THF with one it’s because they got it way back when and refuse to use anything else because of the amount of work that was done to get it.
Like I think my THF uses a dagger I got from Sinister Reign and the Sandung, both of which are already better.