Thesis: Abilities that do not guarantee you will be able to use your transcend are problematic.
Examples: Barrow's Edge's "Drink of my Foes", Noble Branch's "Strike, Breathe, Rend", "Reap the Field". These are conditional on if something else occurs during your turn. In each of these cases, that trigger is a successful strike, though you could imagine the designers' could add other abilities with other triggers, such as you successfully demoralize, etc.
1. One can only use a transcend ability once per turn. As such, transcend is a limited resource. Transcend abilities are strong for their action economy. Therefore, not using transcend in a turn is essentially wasting a strong resource.
2. Putting the divine spark where you might need it next turn seems to be an important part of playing an Exemplar. Abilities where you gamble on being able to move the spark seem counter to this playstyle.
For these reasons, I think the above abilities are problematic in design (the mechanics of Strike, Breathe, Rend and Reap the Field are also weak). One is not sure if they will actually successfully trigger the Transcend in a given turn. So, one might not be able to spend this limited resource in a given turn. One could always choose to just move the spark as an action if the trigger fails, and that somewhat solves the issue with having the spark in the "wrong place" on the next turn, but that's pretty bad action economy in my opinion.
Solution:
1. Redesign these abilities.
2. Particularly for Weapon Ikons, add some feats with 1 action Transcend. that do not require a trigger -- or maybe trigger if a strike fails?
3. I think we need some feats that improve action economy for moving the spark. I think it is going to feel bad if your divine spark is not where you want it in a turn. The Root Epithet's sort of already do this, but it does cost you use the Transcend ability. Kineticist's get the Elemental Blast as part of activating their aura, there could be something similar here.
Thoughts?