One, I would recommend looking in the Heart of Thorns maps rather than the Path of Fire maps initially. Those will also reward 10 points per hero challenge. Two, I would look in the LFG for "HP Trains". Often you can find large groups of people with a commander that will go map by map and collect all of the hero points in a large group.
Tomes can only be used by characters below level 80. And anet ha already said mastery progresion is for level 80s only. A different matter could be those "Writs of Experience" that you get on several of the daily chests. Those can be used by level 80s, so we can't be sure what anet will do with them. Unless all you do is raids, or all you do is fractals, if you play the zones, you'll have the hero points. If you play WvW, you'll have the currency to buy the hero points. Of you spent 2 hours with a train (and I can do this solo on any class, so you know, in about the same amount of time) and unlock an elite spec.