I hope what you are doing is leaving the tanakdin on steelbreaker and then on molgein, and the dk just takes care of Brundir. I don't know if all dks (all 3 specs) have so many interrupts but our dk has an interrupt ready +/- every 10 secs.
The esiest way to get brundit under control is to simply interrupt him, when he is casting something and then pull him in the middle.

