Deathwing has slow energy regeneration, which isnt a big deal on its own. The problem arises when we see that all of his basic abilities cost energy and that there are talents that massively buff certain abilities. We can see he has a lvl 1 that improves blast wave’s damage by 75%, so we can safely assume there are more.
Why is this a problem? Because deathwing’s abilities are directly competing with each other for his limited resource pool. And by the nature of his fire breath, you cannot cast them all because the fire breath will consume as much energy as you’re willing to give it, and is stated to be his best damaging ability.
We can see a similar problem in other limited resource, fast regen heroes like sonya and valeera. As you continue putting talent points into a single ability (like valeera sinister strike) all other abilities get pushed out of use if they have remotely similar roles, because using Blade Flurry means you are using one less sinister strike. Eviscerate is one less sinister strike. This is technically true for mana using heroes as well, but doesnt really come into play unless a hero goes OOM during a fight. Sonya mitigates this problem by having enough fury that she can generally do whatever she wants within reason, and having only two abilities that spend fury, with one of them having a cooldown. Even then, picking a seismic slam build on sonya almost pushes whirlwind out of her gameplay entirely except at times where you must heal.
Back to Deathwing. Imagine for a moment if there is a build for deathwing focused on his fire breath. If it is strong enough its likely people would simply ignore the fact that he has other abilities at all, because those abilties are using energy that could be used for fire breath. It would make his gameplay quite boring.
I know he is not released yet, so things are subject to change, but there’s enough information in the preview video to at least discuss this. I personally suggest removing energy costs for his destroyer and world breaker variable abilities, leaving his energy cost just for his fire breath as an indicator of how long he can use it.
TLDR: Talents and energy could make whichever abilities you dont talent useless.
Thanks for reading.