PE just doesn't sinergize well with many of the BRF encounters and I generally would only take it for Tectus Mythic and use the glyph to reduce the CD then delay the 2nd Fire Ele to the mass AoE phase and nothing else.
Main Reason I take UF on the "AoE" fights is because It doesn't really matter what tier 6 talent you take after ~5 mobs it starts to become a DPS lose over prioritizing Earthquake/Chain Lightning (if you get haste proc from Elemental Blast it might have been worth casting) and those fights usually have a single target DPS requirement, on my logs compared to the others in my guild I'm top damange done to Darmac, and I'm also usually top dps on the Primal Elementalists on the Blast Furnace encounter.
But ye... I generally focus more on single target and then just maximize my AoE/Cleave with Liquid Magma and Earthquakes. You can get high DPS on any boss with any mix of talents it's just more or less knowing which buttons to press depending on the situation and then min/maxing what you know.