How is external LFG superior to an in-game LFG for these issues? LFG parties for heroic raids fall apart all the time.
This is a case of Bungie making things more difficult for no apparent reason.
The people I ran hard mode raids with I met through normal mode LFG runs. I built up a rapport with those people and we were able to schedule time outside of Destiny to be able to commit. Anecdotally, every time I tried to fill a hole in my group either here or on another site for hard it never panned out.