IMO, the aoe battery spender would've been fine if the Queen finisher was AoE.
The problem with gauge spender/shared cooldown is that they are meaningless choice.
3+ target? Press red button. 1 Target? Press blue button. In raiding situation, it makes a button useless. Bio Blaster is set to CTRL + 2 in my case, that shortcut is never pressed when I'm raiding.
In other words, it's button bloat.

You can make it AoE per default, look at Chain saws. No one asks for a single target version of chain saws.
No one asks for a single target version of Double Down, because they works very well on both multi and single targets.

As for "hardest part of your kit correctly"... Wildfire is by far the least difficult part of the job. Respecting Drill and Air Anchor are where the difficulty relies, the more you manage to fit, the bigger the reward.
Wildfire on the other hand is just an empowered Hypercharge phase. You press it, then you follow by one Hypercharge phase like many other you do during the rotation, except you need to press wildfire before. What a gameplay.