elemental damage increase is really really important
think of it this way. assuming your int is 10,000, 1000 more int will only increase the damage by 10% (although it does increase a little bit of AR as well) but only a few ancient items even have 1000int as an option. Also if your level is above 800, since you will only be increasing int with each paragon level increase, the damage increase through int will become less and less efficient. so does element damage increase do alot of work? absolutely. However, if you are using 4 skills with 4 different elements, I would rather choose int over element damage.
A very important thing you need to remember with frozen orb delsere build is that not only do the arrows that shoot out from the orb deal damage, but when the orb explodes, after it finishes traveling, the explosion also deals damage. So essentially what it means is you want to keep the distance between you and minions far enough so that not only will the arrows hit minions but the explosion from the orb will also hit minions. That means zei could be a better option than botp since zei can also stun minions.