Well if the tanks up front are interrupting casters/support, you can do a lot of damage on the tanks who's attaking your support
If you are BG'ing you cannot cast heals at the same time, which imo, makes it seem a bit useless
As for the HoT, I can see your point! It is a lot of hps and very useful when kiting, where the friar is pretty useless if he's staff specced!
It really all comes down to what kind of grp you are planning on running and what you want to use your friar for.. I like the fact that I can do well solo, in grps(may they be small or fg) and that I can also easily go out and do some pve