If slayer works the way she's supposed to work, then the starting energy meta may not be as bad.
Her banner is supposed to only block a certain amount of drain, say for example 1800 energy drain. So as soon as a match starts with bone dragon in the opposing team (and assuming that the dragon slayer team has a full team of 5), that should already be a drain of 1500 energy.
The next 1 or 2 seconds later should, in fact, destroy the banner. If void dragon was paired with bone dragon, the banner would almost immediately be destroyed.
If it worked as intended (assuming the text description of slayer's skill is the intended use), bone and void would have a chance to be able to disrupt insta cast.
However, the damage calculated to the banner is directly blocking the energy drain from the skill itself, so bone dragon's initially only damages the banner by 300 instead of 1500 (full team on slayer's side)...
Imo dragon slayer is OP af... Bone dragon nor void was even a problem with better strats before dragon slayer... Dragon slayer only made it easier