So why doesn't Fortitude overwrite heroic bond?
 

Isn't Fortitude the next line of hp ac buff? But it gives lower hp and lower ac than heroic bond? Am I missing something here?

Fortitude is twice as long as heroic bond... which can be very useful in some situations

One is for buffing newbs while there is no spell restrictions so they have 2 hours of awesome buff, the other is the most efficient group heal you have and a far better buff to hand out to people you xp/raid with. I'll usually give charmed pets fort too so I know I'll never need to refresh.