I came here to complain about this exact issue, if you are going with The Boss Destroyer Build I'm not the highly geared and my Shield Bash Hits 700mil up to 2bil+ with buffs on single target and 500-700mil on group, that If I'm playing but on DB more than 5 targets it will stand if not for the high dps of my follower it will stand there forever, and it will die couple of times and If I'm lucky enough one of them will die and the crusader will keep going...
hopefully there will be a solution for the crusader issues because this is not the only one I faced regarding the combat routine.
Update:as a temporary solution I'm using Guardian instead of Inspire on my Templar (follower skills) so whenever my hp goes down, it would knock away all the targets around me which "re-triggers" the combat...
